There are others on here probably more knowledgeable than I but…
I know of friends who have to change their trolling motor because they bought too short of shaft on it, and in wind/waves the prop would come partially or completely out of the water or would stay in but was so shallow it did not “bite” as well as it should have.
Could this be what you are experiencing?
I cannot speak to the change in performance from 70-80 lbs thrust and if yours is a 12 volt vs a 24 volt like the Terrova you mention.
I remember reading a Minnkota help center article on how to select a correct length of trolling motor shaft.
For comparison I have a 2020 Alumacraft Competitor 175 and the Terrova 24v 80lbs 60 inch works just fine in all conditions.
Hope you get it figured out w/o having to buy a new boat.