New to NAXJA. and i have an odd engine problem

sup guys, Ive been on JF for a while under the same name i have here, and i was pointed this way buy a buddy of mine.

ok so heres my problem, i have a 96 cherokee country that i am slowly building into a DD/weekend warrior.

when i got her she had 235,000 miles and the 4.0 was worn slap out. so i bought a friends rebuilt 4.0 out of his 93 to swap into mine.

well, now that i have the new motor in, as well as a new cooling system. but there is an issue. at around 1500 rpm, the engine shakes. not a violent shake but a vibration that rattles the dash, steering wheel, basically the whole vehicle. I think it might be the harmonic balancer, but when i hold the revs to where it shakes the balancer doesn't look like its out of wack.

anybody have any idea what might be happening? im going to replace the HB this weekend and see what that does. Im just trying to get more opinions.

Thanks

Did you replace the computer also. A 96 computer is OBDII where as 93 is OBDI.