Grinding noise

I dont know if this is the board for the question, but I have a feeling that the problem is result of lifting. If im wrong, im sorry.

When im at a full stop and begin to accellerate something is grinding underneath until it kicks out of first gear. It took a 1200 mile trip to SC for this to happen, but It does and I hope im not stuck with it. Not only can I HEAR it grinding, I can feel it in the floor boards. Automatic Tranny, 4.5 lift. No SYE, and I have not redone the gears.

TIA. Mike.

Look at how far your driveshaft has extended from the t-case (lots of clean yoke showing I'll wager)...

With the rig in neutral (ebrake on) I'll bet that you can MOVE the slip-yoke side to side -- that's likely what you're hearing - that the yoke is no longer fitting tightly to the output splines; so you're getting off-center operation

How did you address lengthing your driveshaft for the 4.5" lift?

How did you address lengthing your driveshaft for the 4.5" lift?

I dont know, I just bought a RC lift and took it to a speed shop for installation. What should I look for? And how do I approach fixing this?