Diesel Bombers - NP271 pops out of 2wd during coast

2003 RAM2500 5spd manual. Put new South Bend Clutch and reman 5spd box in truck. after coasting down hill in 4th gear and then transitioning to flat surface, the transfer case pushes out of 2WD to Neutral. I’m also getting a clunking sound (lot’s of drivetrain “slop” or “play”) when going between load and unload that i didn't have before.

so, i figured i did something to the transfer case snap rings during assembly. not wanting to mess with tearing it apart, i got a reman unit. now the reman unit is popping out of 2wd on the same hills and has even more slop "clunking".

now I am desperate for ideas. new clutch, reman trans, reman NP271 x-fer case...nothing else to replace.

it's not lever adjustment...the shift lever has no detents...position controlled by detents on x-fer case lever.

HELP???