GMC AT4 6.2L vs 3.0 diesel

Excellent info tiller! I may consider using it from now on.

Tiller my truck was almost empty so I filled up with 91. Holy smokes what a difference. The truck was unreal before but now I’ve awoken an absolute beast! I did notice a tiny bit of pinging before but only when I really stomped on it. All that is gone! Whoa I’m going to get into trouble!!!!

Did you have any of the issues that plagued the 8spd? Like not going into 8th gear? Just curious. I never had one myself.

Not that I was ever aware of. I still have the truck but my son drives it and if the boat is pulled, the 3.0 does the pulling now. Just got back from a 1000 mile each way trip to lake Erie and it averaged 13.9 for the trip pulling a 621. I have 3 friends that made the same trip with same boats but they have the 2500 diesel’s and they all averaged around 11-12. I will take it!

Thanks Red! You might have had one after they made the changes to get rid of that problem. It was actually an easy fix, just changing the dang fluid to a Honda fluid believe it or not.

kidfish wrote:

Do you guys with the 6.2L use the 91 octane gas? I thought that’s what you needed to use with that motor?

Thats all I have ever used. 109k on it now and the motor seems strong as ever. The Trans however does not operate like new.

My understanding is a trans flush and new super duper fluid makes a HUGE difference with the 8 speed tranny. Just what I’ve heard.

MX1825 wrote:

My understanding is a trans flush and new super duper fluid makes a HUGE difference with the 8 speed tranny. Just what I’ve heard.

A flush or just a gradual drain and fill?

LabDaddy1 wrote:

<div class=”d4p-bbt-quote-title”>MX1825 wrote:</div>
My understanding is a trans flush and new super duper fluid makes a HUGE difference with the 8 speed tranny. Just what I’ve heard.

A flush or just a gradual drain and fill?

On the 6.2 and 5.3, I would pull the pan to drain that fluid, add new fluid(slightly overfill) then pull the hard line that runs into the transcooler(it runs through the radiator), start vehicle up, put in gear to the pump with run and push most of the old fluid out. Once the fluid starts to “clear up”, shut down, refill and repeat until you’re happy with the results.

One thing, to pull the pan you need to either remove the y-pipe or you can also get creative to “move” it out of the way. There is a flex pipe that give you just enough room to pull the pan when you give the exhaust a little persuasion.

You can just stick with Dextron HP(8 Speed) or VI(6 Speed. Also, Amsoil makes a ATF that is HP equivalent. You’ll likely need about 10-14 Quarts to do the method I described above.

I would never flush a transmission. Drain it, replace filter and refill. A pain, yes, but you are not pushing metal and lord knows what else throughout the system

Yeah, flushing any sort of fluid in a motor is kind of foolish. I wouldn’t be worried so much about metal, if you have pieces large enough to clog up a passage in a auto tranny, then you have bigger problems. But you can dislodge debris/dirt/sludge. Even more so, the benefit is what? You don’t flush motor oil out of an engine to get every last drop, although I have seen some advertisements for this process. Every fluid can be just drained and call it good.

This thread reminded me I need to do an fluid change on my transmission before I head to Canada next month.

Thanks much for the replies and loads of information!

I ended up getting the 3.0L diesel.
Hopefully I can post the pic with this reply.
It came down to availability and price.
They have 2:1 ratio of diesels over gas in this model on just about every car lot.
They also charge an extra 1500 for the 6.2L and get this, 350 for an option that lets you tone down the sound of the exhaust on the 6.2L.
So with tax, almost $2k extra for the gas engine. Totally the opposite from what I’m used to seeing.

Again, Thanks for all the information!!

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The exhaust is not that loud on the 6.2. My son has a older 5.3 with some aftermarket exhaust that isnt obnoxious and its way louder than my 6.2. I kinda want to add some growl.

CaptainMusky wrote:

The exhaust is not that loud on the 6.2. My son has a older 5.3 with some aftermarket exhaust that isnt obnoxious and its way louder than my 6.2. I kinda want to add some growl.

What I thought too and to have to pay extra for the option to tone it down…crazy.
That’s 1 of things I liked about the 6.2 !!

BTW thats a beautiful truck! The diesel is a wise purchase now since its less that gas! Is that the titanium rush metallic?
My son details at Miller in STC and he said that is the best possible paint color to work on because it is so easy. Of course mine is the hardest LOL

Thanks!
It was either Titanium Rush or the Volcanic Red but the TR was a standard box so I opted for that one. Not many Standard boxes available. Well, in white or black there’s a few but still tough to find around here.

What’s the hardest color to work on?

CaptainMusky wrote:

The exhaust is not that loud on the 6.2. My son has a older 5.3 with some aftermarket exhaust that isnt obnoxious and its way louder than my 6.2. I kinda want to add some growl.

The borla I put on my 5.7 hemi was a fantastic sound. Couldn’t hear it at highway speeds but had a deep rumble when you wanted to make noise. Borla did a excellent job on there options for the hemi. The magnaflow I had first bought came off after 2 days.

Nice looking rig to the op

haleysgold wrote:

What’s the hardest color to work on?

Pacific Blue Metallic! My son spent hours on it! He is very meticulous though and yes, he is my son, but he is the best one they have. The Gillelands who now own it request HIM to do all their personal vehicles including Christys 140k Escalade V.

BC I have heard Borla is the way to go, I might have to check into them. I certainly dont want a drone on the highway so that is good to hear. My sons has a bit of a drone which gets a bit annoying but its not overly bad.

CaptainMusky wrote:

Pacific Blue Metallic! My son spent hours on it! He is very meticulous though and yes, he is my son, but he is the best one they have. The Gillelands who now own it request HIM to do all their personal vehicles including Christys 140k Escalade V.

Next time you see Christy tell her she still owes the guy with the Blown Black Formula $100 after I walked away from her in her 4th Gen SOM Camaro.

Are you looking to just make noise or more power? A catback won’t net much of anything, maybe 5-8 RWHP. Throw a set of 1-7/8″ LT Headers on a 6.2 and you’ll gain ~25 HP and ~20FTlbs of Torque. I assume your 6.2 is a LT1?

TillrLife wrote:

Next time you see Christy tell her she still owes the guy with the Blown Black Formula $100 after I walked away from her in her 4th Gen SOM Camaro.

Are you looking to just make noise or more power? A catback won’t net much of anything, maybe 5-8 RWHP. Throw a set of 1-7/8″ LT Headers on a 6.2 and you’ll gain ~25 HP and ~20FTlbs of Torque. I assume your 6.2 is a LT1?

Haha that is awesome! What vehicle was she driving? Im not sure what that is, do you know approx year? If it is the SS or ZL1 my son detailed that thing and he was scared to death because in the parking lot it was going 30 with his foot off the gas.
Im not really looking for performance gains just a deeper tone. It does sound nice but even a stock Ram Hemi has a nicer sound IMO.

CaptainMusky wrote:

Haha that is awesome! What vehicle was she driving? Im not sure what that is, do you know approx year? If it is the SS or ZL1 my son detailed that thing and he was scared to death because in the parking lot it was going 30 with his foot off the gas.
Im not really looking for performance gains just a deeper tone. It does sound nice but even a stock Ram Hemi has a nicer sound IMO.

It was a 2002 Camaro SS, SOM is Sunset Orange Metallic. This was quiet a few years ago. I told her I would run, but it would cost $100, she said ok. I believe her car was mostly stock, my Formula was making 530RWHP.

ZL1s are a fun car, the 6th Gen Camaro is far better than the 5th Gen, but still not my cup of tea. I’ll stick with Y-Bodies.

OK yeah the one he drove was definitely 6th gen.