My 1999 1500 Suburban 5.7 has 25K miles on it. It hesitates under hard acceleration. It runs smooth under light acceleration. Recent work includes new plugs, wires, cap, rotor, coil, both catalytic converters and both 02 sensors behind the converters. The sensors in front of the converters are original. Also, the intake had been off twice. First time to fix a coolant leak and the second time to fix a vacumn leak cuased by the first repair. The vacuum leak causes the trans to up-shift very firmly. The up-shifts are no slightly firm on occassion, so I don't think I have a vacumn leak. Another symptom is this. The last change was the cap and rotor, after which the engine ran smoothly, and the check engine light went off. The light came back on and the hesitation retunred in less than 500 miles. I removed the NEW distributor cap to discover that the contacts and the rotor were charred, as if they had a lot more miles than 500. I cleaned the contact and it ran better, but has started getting rough again. Planning to inspect the contacts again this weekend, but I suspect I have other issues. I read on another forum about valve guides wearing past 100K on these motors, which could foul the plugs. However, when I have experiecned similar issues with other vehicles, it was always a problem with the ignition system. Need some help please. i am a pretty fair backyard mechanic, but I am lost. I am happy to swap knowlege with anyone. I spent 14 years in the car stereo industry, so I can offer some solid help to anyone needing it with their audio/video/security systems. Thanks! Jeff T.