Re: How much weight towed with a 98.5-01 Cummins dually?
 

I believe going from a 3.55 to a 410 the carriers are different. From what I have found so far. It may be more cost efficient to replace the whole diff with a used one.

Re: How much weight towed with a 98.5-01 Cummins dually?
 

I would be worried about the NV4500 5sp trans when pulling heavy. I grenaded 2 of them in my 97. I went to a NV5600 6sp and never a problem since.

Re: How much weight towed with a 98.5-01 Cummins dually?
 

I also blew up 2 NV4500 transmissions in my 1999 24 valve CTD and I hated the gear split going down from 4th to 3rd and trying to get back into 4th gear. You couldn't get enough RPM in 3rd gear to get into 4th gear without loosing all of your boost.

I was looking at buying a US Gear Aux Trans, but I found a place on line that had a full conversion kit to swap out the NV4500 for a 6 speed NV5600 with the big input shaft. Best thing I ever did because they made it an easy swap with flywheel, pressure plate, disc, fluid, trans mount adapter and an extender for the speedo sender on the trans..

By the way all of the parts came in MOPAR boxes including the trans fluid.

I tow about 13,000 pounds with a 3.55 rear gear. Even up and through the Eisenhower Tunnel at 11,200 feet

Re: How much weight towed with a 98.5-01 Cummins dually?
 

The weak part of your truck is the NV4500 trans. If you are pulling heavy beware of towing in 5th gear. I blew 3 of them up in my 97 before I put the NV5600 in it.