So since it's been hot enough to run the AC in my truck, i've noticed a problem. Any time i'm sitting at a stoplight, i can feel and hear the engine dropping a cylinder. It's to the point where it shakes my truck slightly when it happens, and it's getting rather annoying. It will also sputter intermitently upon accelleration, but only through first gear. Tow/Haul seems to make it a little better, but it could just be my imagination. I changed the plugs from the Autolite Platinum plugs that were in it to a set of Delco Platinums, and it seemed better for a bit but it's back to the way it was. It's pissing me off and i'd like to figure out what is causing it. No CEL either. Any ideas? Truck is a 2k Sierra with a 5.3, with about 90k on the clock.