Vibration search question

Working on a 2006 Kenworth T2000 C15 mxs 475hp/18 speed/Ag400 Dsp40 3.36 rears 930k looks to be all original.It has an uneasy vibration/shake felt up through the Trans and floor going down the road in any gear, and only when applying throttle. Checked the basics like yokes,ujoints,carrier bearing, driveline phase,oil levels any noticable issues with frame/suspension components,motor mounts tight,exhaust not touching frame, no yoke seal leaks or high temps in tranny,rears or hubs. Ride height valve is working.. tried to verify proper measuring procedure for this model with kenworth and they wouldn't tell me anything due to supposed lawsuits. The ride height linkage looks original, I get a measurement of 8.50" from top of weld on inside of rear axle to bottom of frame. But unsure on correct procedure... after looking it over the only noticeable issues I saw was the carrier bearing housing had a spot rusted through not any play in bearing itself but definitely needed to be changed so I replaced it with a Timken and got it mounted as close as I could in relation to the one I took out. I replaced the shocks as they were definitely shot. Noticed a little bit of up and down play on input bearing on front rear(dsp40)(yoke was tight) and a small oil leak on top of diff mounting flange which I think was allowing some water in the front rear diff. Oil drain plug had some shavings and oil was a little milky. I figured since I had to slide the diff out a little to reseal it I would just take it right out and take it to a gear shop to inspect the power divider and everything else thinking it might be part of the vibration. Doesn't sound like there was a whole lot wrong it. Now while I have the diff out I was wondering about the play in the output shaft bearings. Is there supposed to be much side to side/up and down movement in the output shaft bearings for alignment purposes? I'm not getting much in and out play on the shaft end but get quite a bit side to side. Probably a good time to just change them but wondered if that was normal. Thanks

 

Probably would be a good idea considering it looks to be original. I kinda thought if that was real bad it would feel a bit off balance or something idling and run through the rpms while parked but this is pretty smooth through the rpms.

 

Did you figure it out by having the driveshafts balanced?

No I haven't had the clutch out, not much history on the truck but a lot of it still looks like original parts but not abused. For all I know it could be the original clutch, the rubber pad on the clutch pedal doesn't look like a foot spent much time on it. The clutch doesn't seem to be slipping, holds good adjustment and engages smooth and transmission shifts smoothly through all the gears high and low. Is there a way through the inspection cover I can tell if it's been replaced?