In the mid 2000 era, the auto trans were improved drastically. 97-2002 not so. If you are going to be towing weight over 6,000 lb's I would recommend the manual trans. The only problem with the 5-spd. manual trans was 5th gear spinning off the shaft while overworking it under load, towing heavy. There is an update on the 5th gear secondary shaft where a clamp nut can be installed to stop this from happening. I own a 96 2500 diesel truck (juiced up) with the 5-spd. and have not had any issues with 5th gear, even towing 13,000 lb. However when towing a ton of weight uphill, I downshift to 4th.