I am on my 2nd NV4500 in my 99 CTD and had the first one out at 100k to put a clutch in it and at that time , I took the back of the trans off and cleaned and tightened the nut to 250 ft-lb with Green loctite and re-staked it and that went to about 185K when the trans failed (my fault) because I used the wrong oil/lube and trans failed, did not have the 5th gear nut come loose. I found in the Mopar Box , a new NV4500, so I replaced instead of rebuilding it and in the Mopar box it came in I found a 4X5 note card with "5th gear mod" printed on it, so I thought all is good and put the new NV4500 in and that trans went to 240K and 5th gear nut came loose and I have only gone 8 miles since that happened. The mechanics I have talked with say to tighten nut to 400+ ft-lb with green loctite and re-stake it and then put the spline nut keeper on. re assemble and drive on. This will be my daily driver and I have a 2016/17 2500 CTD that I use for towing toy hauler ( 5/6 snowmobiles) about 11k lbs and stays hooked up here all winter and then hauls 4X4 atv and side by sides periodically all summer on smaller trailers So that is where I am at , ready to start this job by first getting the T case off and go from there!
Sorry for the long winded story here!
gtwitch in wyoming