I've read through most of the threads from others having towing issues but haven't quite seen my problem. For reference my truck is 01 gmc 2500hd stock other than a 4 inch exhaust and an intake. Last year I had issues with the truck going into limp mode when hauling a trailer and normally only going up a hill at highway speeds. It would throw a large fuel leak code dont remember the exact code but found a leak on the driver side where the fuel line threads into the ported fuel line fitting. I replace the ported fitting with another and everything seemed good until now. Hauling a 13ft enclosed trailer running up hill the SEL came on but the truck ran fine until I came to a stop at the off ramp. When I went to take off the truck went into limp mode. I pulled over and plugged my scan tool in only for it to say no codes detected and the light magically went out. Truck ran fine the last couple miles to my destination. I'm baffled that the code just dissapeared and nothing was saved. I did shut the truck off before plugging in the scan tool. Have climbed all over the truck and no signs of a fuel leak and no smell of diesel anywhere. Anyone have a similar situation with no codes to work off of?