Hi guys I have a 05 Fx4 5.4, Just recently bought a 17ft boat.. And i notice sometime my truck shutters from 1st going into 2nd.. its almost like it doesnt wana make up its mind should i go back to 1st or 2nd and it shakes?! its only got 40,000 miles on it.. and it will only do it while towing or under a load and sometime when i give it to much gas when its trying to shift 1st to 2nd.. Really bugs me!! Pls Help?!

 

It sounds like drivetrain wind up/pinion angle, especially if it happens while towing (weight on the rear of the truck changes ride height, which changes pinion angle). It seems to be exaggerated IME on Supercab trucks with two piece driveshafts.