I use a can of Seafoam every so often to clean the throttle body, but this doesn;t seem to help the problem. I have checked the air filter and was surprised at the low level of dirt I found on it, so I don't think that that is the problem. Transmission is automatic. I really haven't done much work on this truck and didn't do any on its predicessor, a '04 w/manual tranny. I just kept taking it to my dealer, but now its paid off, so I plan on doing more with the truck (when I'm not working on/riding my motorcycle). I'm ashamed to admit that I didn't even know how to access the plugs-prior to my first Colorado, I did all the work on my '91 Isuzu SpaceCab! I have the factory manuals for the '04 (figured they hadn't changed much in three years-do you recommend the Clymer's?