I'm posting again about the 1998 silverado 4x4 k3500 with the 5.7 vortec. I had the posting about the backfiring issues during deceleration. All of your advice was rock solid so I'm looking for more info from chevychase and dirtrider. Not sure how to contact. Tried to add chevychase as friend. At any rate, I did as instructed and the truck is running very nice. Accept now it's really weirding me out. I replaced the MAF sensor and it cured the issues it was having. But the service engine light wont go off so I go back to parts store and scanner says MAPressure low. So I buy a new MAP sensor and change it out (yes battery was disconnected) the light goes off signifying no problems and I get it out on the road home and it goes right back to doing what it did before I changed out the MAF! Kicking, sputtering, backfiring on deceleration! Brand new parts! What gives? I take the new MAP out and put the old one back on and it seems fine again but the service light comes back on and I did this twice with two different MAP sensors both brand new! Should I drive it over ten miles and see if the PCM will relearn to accept new sensor? What do I do? I just want it to be fixed! Why would it go back to doing that with NEW parts?! I just need to know what to do. I'd appreciate the help fellas. Do I need to get something done to the PCM?