I dunno, U.joints, trackbar and ball joints, sounds to me like it's treat this as a complete tear down and review/replace bad parts time to me.
Take and find a level spot, preferably cement or tarmac, maybe jack the truck up level and do some critical measuring plumb lines from the axles center lines L to R and F to R measure for square? may be an idea to remove tyres to get this as accurate as possible make sure both sides are equal, front to rear, also make sure axles are centered correctly L to R once your sure of the trucks position as it should be SQUARE then start the isolation of parts.
Pull front drive shaft?
Pull the axles in the front diff, 1 at a time-test without axles?
Basically start removing removable parts to isolate what causes the issue one part at a time.
If after removing drive shaft and axles your still having the problem, move on to things like shackle bushings all 4, and the track bar too. pull and check for the squishy bushing?
If none of the above? Try Ball joints, tight,but no binding in any direction of travel? Replace if needed.
Isolate one part/system at a time. That is my best recommendation.
Good luck
EDIT...another thing...Check for cracks along frame or any suspension mounting location or loose rivets too.