Cherockee

I am sort of new to ZJ's but have and do own a few XJ's and even have had one that I installed a lift on, so I know my way around these trucks.

I have a friend that has been having some transmission trouble lately and we're letting a trans shop deal with that- started out as needing a new torque converter and ended up getting a completely rebuilt transmission too. We are now in the process of making our thrid trip back to the trans shop as it feels like the trans slips while traveling at highway speeds.

Anyways, on to the suspension trouble. The vehicle in question here is a '98 niner, 249 TC, 3.5" Rubicon Express lift kit, t-case drop kit, 245/75/16 AT tires. Lift has been on for almost 2 years with no real issues, although I did find some loose bolts this past summer. While at the trans shop the mechanic said the front driveshaft was rusted very badly and wouldn't slide on the splines. He cleaned that up and lubed it but informed me that both drive shafts were hammering the TC because they're too long (the front only because it was rusted and wouldn't slide on the splines), implying that when the vehicle was lifted it brought the driveshafts closer to the T-case. In the XJ arena I have never heard of shortening a d-shaft, but didn't know if this is a problem just for ZJ's. He put the Jeep on the floor lift and showed me how the rear slip yoke was fully compressed into the t-case. Is it possible that the lower control arms are not adjusted correctly? Is it possible to remove the front driveshaft and drive around without it connected with a 249 T-case? How about rear d-shaft remove? The other issue that has developed is a lot of vibrations since the tranny rebuild (t-case drop still in place). Trans guy says the vibrations are our problem and he's alread done more work than he's been paid for.

So what other things can be done to reduce driveline vibrations (aside form the typical maintinence of u-joints)? I've read here that a np242 should bolt right in (if from a comparable year), but how about the np231? I think he'd like the idea of staying away from a viscious coupler as they seem to give a lot of people trouble. Any thoughts on this?

Thanks for reading such a long post. I appreciate any constructive answers you can provide.