Okay so I bought this from a reliable friend. 72k miles and the thing is mint, well kind of. It started throwing codes and I checked forums and people said oh it's plugs wires distributor cap and rotor camshaft sensor. So I replaced them all (basic tune up whatever). It had a rough idle and wild stall every now and then sometimes just sputter and it would refire on its own. So it starts throwing a cat code. So I had my cat replaced professionally, they also removed the mini cat... still idles hard and stalls every now and then. So I get pissed and bring it to a shop. They diagnose right away that injector #3 is no good, boom I get the blazer back and the idle is mint. So I'm happy. I've seemed to gotten my power back and zero idle issues. I wake up and go to work 5 miles down the highway. Stalls again. But this time it doesn't refire on its own and as I roll to a stop it backfires maybe 5-6 times. Once I'm at a complete stop it fires right back over and no issue for the last mile... engine light comes back on throwing cat P0420 is the only code. Please help before I push this beautiful piece of **** off a cliff thanks. I also replaced one of the three o2 sensors