I recently replaced the intake gaskets on my wife's 99 Tahoe (5.7/auto). After doing so I had a reputable shop set the timing since I don't have that fancy computer. Now 3 days or so later the "service engine soon" light comes on. The truck feels like it has not low end guys at times. This sounds like timing issue to me, but I would like a second, third, or 100th opinion lol Here are the codes that we pulled: p0420/p0430. I've read that these are generally O2 sensor or cat converter issues, but again I would appreciate confirmation from those of you more knowledgeable than myself. Thanks in advance!