Ramcharger vibrates after using 4wd

I had my friend that has been rebuilding gear boxes and T cases for 40+ years take a look at my T case. There were no issues with it. Now the front drive shaft (aka prop shaft ) was another story. The cardon it’s the “H” double yolk with 2 u-joints, the u joints were toasted. The shifter detent might be stuck. Other thing is the 241 case is hard to shift when not spinning
I replaced the detent spring and flushed it several times, but the selector is still seized up real bad. There’s hardly any rust on the truck but any aluminum looks calcified beyond belief. It’s the NP 231 (I believe it’s aluminum). Flaky and scales all over. A lot of corrosion. Best I can tell is the selector is stuck internally, as I soaked it in PB blaster and smacked the linkage back and forth a million times with a hammer. Wire brushed around the selector bolt that goes inside. Hard as **** to move it still. Got it where the front was disengaged and drove it home. With it being in 2wd, would the front driveshaft / u joints still cause the vibration. Like OP said, there’s nothing in my steering wheel. No shakes, shimmy or pulling.

Sorry to hijack, hopefully this gleans some new info for OP too.