I need some suggestions on where to look . First i have a Z-71 which comes with a towing package . Its 1998 extended cap . Now I bought this truck with 17,000 miles but had a 5 yr. 85.000 warty. the rear end has been replaced, also a New Trans. all factory . I put dual tail pipes on it took the mufflers off put glass packs on it . the problem begins when towing a boat was the first time I notice the loss of power and the engine service light would come on .. to make the story short . I had a dealer to tune it up, you know connected to to the machine and all told them what and how it was acting . about 600.00 dollars worth but still the problem was not solved . They came up with all sorts of things but the real problem . They wanted me to go to house hung up my trailer and pull it up a hill to show them what it was doing ? Can you believe that ? I knew right then these people were trying to blow smoke up my a--. I got tired of messing with them summer was over and I wasn't pulling a bout or anything so I forgot about it, big mistake. Its my sons truck I bought it for him for Grad. but still the dealer should have qualified technicians to perform at that price . Anyway when pulling a trailer it loses its power and the service light comes on as before . I could have kelp the 600. at least I would have money for tow . Have any of you guys have an idea what the problem could be ?