Find some stock tire/wheel assy's to throw on it and see what happens. I'm thinking even with the 4.10 gear you are achieving a low enough rpm when you "back off" to where the engine is having difficulty getting the taller larger rolling mass to move. Sounds like you better start whacking away at that wish list in your sig to move the power level up.

 

Look in the turbo inlet for oil. My truck was weak with oil residue inside. The dealer replaced it under warranty and now it runs great. I can get 28 psi of boost out of a Hy.

 

Don't give him any ideas.