jland

I hav an 88 cherokee 4.0 231 t case and 5 spd manual tranny. when in 4 high it doesnt make any noise or popping but when i put it in 4 lo and try to climb a hill it pops and grinds in 1st and 2nd gear but whn i put it in reverse it doesnt pop or grind. I checked the linkage and thee front axle and vacum lines all seems ok. I replaced the transfer case just the other day and it is still doing it. I also split the case halves on the old t-case and all gears seemed ok there was parts of blue plastic in the case and i seen where the chain had rubbed against the case just a little bit. Im not sure what to check now???