[justcuz]

I used to see that on a lot of early F-250's. The front driveshaft would be slowly rotating driving down the road...at a speed that was not directly related to wheel speed. There is only one guess I have on this happening and that is the circulation of oil in the transfer case has a parasitic effect on the front output gear and spins it slowly. The oil is the wind and the front output gear is the blade of the windmill. If you had a clunk hitting bumps I would have guessed slip yoke right away. I found out about greasing output splines on slip yoke when I had that clunking on the Blazer. Transmission shop guy clued me in to it.

I am slowly learning a little about diesels, when you leave the black signature when you accelerate does that mean you can up you turbo boost pressure a little, or is the black just momentary? The Cummins from my research seems to be the most cost effective diesel from a reliability and ease of modification standpoint for light duty trucks. Seems like you made a good engine choice.

Its amazing how just a roughly 10% reduction in engine speed can make such a difference in the way the truck runs. Basically if you ran 35 inch tires the 4.10 would have been fine then. Reason I ask is I am thinking of building a diesel off roader in the future and plan on roughly 35 inch tires with a 4" lift and some fender trimming. Its gonna be a square body Suburban or longbed pickup with a shell.