I have had good luck with adding a gallon of aviation 100LL to each tank when I fill the GMC up. The 100 octane give me a small boost on the anti-knock factor and I feel better knowing that I'm running at least some lead through the stock 302 mill. I get the 100LL from a buddy who works at the local airport FBO. The stuff he gives me is fuel sumped from aircraft needing fuel tank work. Legaly it can't be put back into the aircraft because of storage requirements but there is nothing wrong with it for the truck! smile

"The Operation of GMC trucks is normally smooth and steady, with no loud rattling, knocking or unusual noises. A good driver will quickly become accustomed to driving a GMC truck and will get the feel of his vehicle regardless of his engineering knowledge."-TM10-1563