Shouldn't be a problem using a different rearend. No trannie swap required. You'll have to find the correct U-joint to make it all work though. Of course you'll have some cutting and welding time installing new spring and shock mounts. Just food for thought, going with a 3.42 rearend drops your RPM's 700-800 vs. the stock 4.57 gears. A 3.73 will drop the RPMS about 500. Is an overdrive really required at that point?
