I have a 1999 suburban with 150K miles. It shifts fine at first then shifts very hard after it is hot. I fixed it by replacing the valve body and all 5 shift solenoids. It works better then new. If the tranny acts up and you stop the truck, shut it off , wait 4 minutes then start and go again and it works for a while then it is solenoids that are sticking. The valve body and controller on mine was full of gunk. 2 of the solenoids were bad. A new valve body replacement kit with gaskets and solenoids is $189.00 $200 to replace. Total $389.