Two things I'd check

1) the driveshaft/u-joints, new u-joints and balancing should run about $150-175

2) the transmission - likely primary shaft wobbling in case. This could run $500-1500...

"Does this part need to be in there?"

1996 Dodge 1500 single cab / short bed, 5.9 4x4; 2" lift (springs not blocks), C.A.I and more mods to come.