If it's a Jeep it's a 3550.
There's info on Wikipedia.

Here's the Novak Gear writeup.
https://www.novak-adapt.com/knowledge/transmissions/manual/nv3550/
Novak is big in the 4WD world and they don't seem to think the 3550 is so bad. The only transmissions they talk about for swaps are granny low 4 speeds from fullsize pickups or larger. This is for the rock-crawling crowd. Giving up the overdrive gear for a Jeep driven on hard surfaced roads would be a mistake, IMHO.

Remember the three most dangerous words, "I have heard."

R.