I also was wondering about the swap to nv5600. I gotta 99 cummins with the nv4500 and i run it as a hotshot truck. So im constantly hauling loads up to 12000lbs. The trans only seems to hold up for about 6 months before having to be replaced. Had one rebuilt with a heavier shaft and gears and didnt seem to make a difference. Was wondering if the 5600 would last longer and hold up better or if its not worth it. Also if yall have any to sell let me know a price. Been gettin reman 4500s for around a grand.

I have hauled 6 or 7 10,000 lb shipping containers in the last 6 months and can't say as I have noticed any issues with my 4500. Granted I only pull in 4th gear when i have them on the trailer but if I had to guess i would say I have between 16 and 20,000 lbs behind me with trailer and container. Only issue I have is keeping the temp under 210 pulling through the hills. The transmission seems to handle the load nicely and I have done no upgrades to it with the exception of a southbend clutch. As far as the original posters question i believe I read up on it once and thought you had to change driveshafts as well as crossmember or atleast member location because the 5600 is longer. To this point I still have not had the chance to do a swap so time will tell.