The more I think about it it sounds like driveline vibration for sure. I put a 8 in lift on a short bed Chevy once. I bought a nv4500 for it and a adapter for a 10 spline 205 t-case. The lift was all spring a super lift kit no blocks no body lift mine acted like yours I woulda bet the farm the tranny was bad I lowerd the t-case 3 in messed w pinion angle it didn't change. I would drive it and stop get out and feel my u joints the pinion the back of the t- case to check for something hot it was always the back of the tcsase. I got a high angle 1 ton cv shaft and the problem was cured. If your getting a vibration something in your drive line will be hot. Drive it for 2-3 minutes at the speed it vibrates pull over make sure you have your gloves on and check those spots I mentioned above and also where you 2 piece drive shaft goes together one spot will b considerably hotter than the others then we can go from there. If u had a spare front shaft you could rig up a temporary cv joint rear shaft to see if that helped it jst lay it in a piece of angle iron and weld it up it won't be balanced but it will b straight and put the cv to the tcsase not the pinion. If it were mine that's how I would go about it. Throwing money at a high angle cv is very expensive if you are not 100% sure that's the problem let us know where you think the " hot spot " is. Good luck don't forget the gloves !!!
thanks for the tip. i'll test that once i have the new cv ball install... i have apart now, and the cv ball is F*@$% UP....
