Check the easy stuff first
Tires...
One could have a belt separating,look for unusual wear on the tread,have someone slowly drive the truck while you watch the tread on each tire,look for a unusual bend in the tread.
90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews