My truck was still warm when we did my headers. We really didn't have a hard time though. The main problem was being able to get to them in a position to put any kind of decent force to twist them off. There where a couple that seemed to take everything I had, but we got them. I do remember one getting to the point where I thought I was about to round 1 nut off, then it magically came off lol...Must be because your truck has so many miles? I know one thing we do at my job, whenever we run into pesky screws or nuts that don't want to budge, we hit the hell out of them with something heavy to loosen them up. Take something long and place it on the side of the nut, then take a hammer and give it a few whacks. Maybe it will help jolt the nut a little loose so it will turn off easier