Help.....Vibration

i have a 2000 chevy silvy 2 wheel drive ext. have a rotational vibration at 55 mph. What i have done, brakes all the way around,new drive shaft,carrier bearing,universals,tires,oil changed to synthetic in rear end,locker addiditive to rear end,now they are thinking front wheel bearings anybody else have this problem costing alot of money to stil not be fixed. at least i am only paying parts which i know they are not marking up because wife works at place they buy the parts.

is the viberation in the sterring wheel or in the seat that will tell you where to look front or back and its not uncommon to get a bad tire or once the guys that mounted one for me dropped a weight inside and it beat the hell out of the inside of it

in front steering and dash not that bad but noticeable. changed to different tires fron anothe truck still same

Might just be frame beaming. Normal condition.

If you have a vibration, the proper way to diagnose it is to use an electronic vibration analyzer or a reed tach and get the frequency of the vibration.
Next compare that information to some mathmatical calculations for componant rotational speed and this will tell you what componant rotational group is the source of the vibration