Yeah. Driveline clunk will only get worse as the wear get ls worse. At some point the differential will grenade.

It could be a loose pinion nut. It could be bearings. It could be backlash or the mesh.

With the transition, it could be all electrical. It could be in the valve body or maybe just clutch pack related.

But with it being an 02, likely high miles and being pushed to 5500 "to merge into traffic", it won't last long if continued.

 

I'm thinking the rear end is probably just the u-joints with the clunk... But this doesn't explain the whining effect happening. Also, typical dodge thing, when i changed trani fluid and checked the level it was in park not neutral, therefore giving an off reading. Re-checked it today while in neutral and it wasn't full, but not empty. Gonna add a pint or two.

This would make sense why the truck would jump to 5500 rpms while the mph didn't jump with it. While merging, the fluid shifts to one side of the pan,left, and if the fluid is pumped from the right side if the trani is low on fluid it would be sucking air causing that problem. Still doesn't explain why it doesn't shift at high rpms. If its sucking air I can see why, but not sure on the whole not shifting into 4th or whatever gear it would be in around 50-60mph.

 

The gear fluid I used had the modifier already in. So yes.

 

Most transmissions shops will check everything out for free. You might want to schedule an appointment.

Finding a shop that specializes in differentials can be hard but I suggest you look at that also.

Only other thing I can think of is if you have a tuner on the truck or have the O/D switch disabled and even then IDK if that would affect it.