My 2001 2500 4x4 with a duramax and Allison has developed a problem when towing a load. If I hook a trailer to it and put a load on it the truck goes into safe mode and we have had every test done that we can thingk of. A GM rep even used this truck to teach a class with and found absolutely no problems with it. Initially the mechanic thought the after market air cleaner we had was too small so I put a much larger air cleaner on it. any suggestions, anyone??