I got a 96 Blazer with the HighOutput 4.3 Vortec recently. I have installed all four new O2 sensors and also an EGR Vavle all of which the original equipment was bad. It performs significantly better...but I still get the SES light when I run it real hard for a mile or two, or when I roll it up around 75-80. It lose alot of power, and have almost no acceleration unless i have the pedal to the floorboard. Also shifting gets screwed up, I wont get second gear till like 35 then it kicks it in real hard and if on gravel it leaves scratch marks. Do you guys have any idea what it could be. Ive also had a friend reset my system with his OBD2 thing a few times and it works great till I run my Blazer hard enough to kick the SES light on.