My brother and I both have 2000 Chevy crewcab duallies C3500 with the last of the 454s. We are both experiencing a severe case of ball lessness when towing. Both used to be great tow vehicles towing anything but lately and intermittently, the trucks will barely go 25 up a hill even with a small trailer. The dealers say there is nothing wrong, I have had O2 ensors changed thinking that was the problem, If it was the Cat t would be all the time, but it feels like a clogged cat when it is happening, the more gas you give the less power I have. It is embarrasing. Ha anyone had this problem before and what cured it?