I had a hard time deciding in 2003 between the Duramax and the 8.1. I chose the Duramax but was never sure it was the best choice. Both have the Allison transmission and a lot of power. The additional maintenance and initial cost of the diesel was more than the fuel savings. So I am still not sure I made the right choice. How is the interior? Those trucks are not known to be leakers. Mine doesn't leak into the cab at all and it's an extended cab like that. So hopefully the interior is good. The metal brakes lines were bad on those and rusted. There are several stainless kits that include braided stainless flex hoses. I put one on mine before they went bad. I don't drive mine much anymore but I still have it. I bought a 2020 1500 Trail Boss with a 6.2 for a daily driver. It gets about the same fuel mileage empty and premium fuel it takes is still cheaper than diesel. We use the old truck for towing our RV because it gets much better mileage towing although there is no noticeable power difference towing. Both pull it effortlessly. The 1500 just uses a lot more fuel. Also I have a canopy I put on the Duramax for all our stuff when we travel. Other than that we just use it to haul heavy stuff or pull trailers with loads that exceed the wimpy hitch rating on the 1500. Also I drive it when it snows so the little lady can drive the 1500 instead of her car. The 1500 is great in snow because it has the auto 4WD. That works much better than normal 4WD on snow and ice. As long as it's in auto not 4WD anyway. Plus she can just leave it in auto when on clear roads where the old truck needs to be switched in and out of 4WD. So I have good reasons to keep the old truck but I would have anyway because I have always really liked that truck. If you fix that truck up I think you will really like it. The one other thing you might want to change is the trailer hitch. They were really weak and the same hitch as the 1500s had. I put a draw time class 5 2" on mine so it can tow to capacity with a bumper pull. The stock hitch is not rated even close to the trucks rated towing capacity and the pin hole elongated in it anyway.