I've noticed a shake when pulling up hill, it feels like the road is rough but if you pull off the throttle it smothes out. I run a EZ unit and pull a racecar trailer loaded about 8,500 LB. The power is good and milage is great. I have pulled the EZ from 3 to 2 but does not feel any different.

 

Sounds like the torq convertor slipping . IF its stock it wont last long with any hp inprovements. Stock convertors are very good at all,,, upgrade it and a decent valve body in the trans will make it a whole new truck for pulling

 

I do have aftermarket billet converter and trans was built 2 weeks ago.
thanks for the reply