I say go with the nv 3550. You can find replacement parts at any transmission shop. Cause this was also a worry of mine before I made the swap, and also I seen about 4 wrecked tj in a junkyard with the nv3550 in them. The transmission is a daily drive. It doesn't shift as smooth as other transmission like the top loader 4 speed, but it doesn't have that huge truck feel like the np435 , or nv4500. But you can run threw the gears really quick if you want to have some fun.