i have had these problems on other LT1s that i have owned in the past and here is what i learned...spend $89 and take it to the dealer and have them tell you exactly whats wrong with it or...you can take and spend hundreds of dollars on cats, pumps, sensors, opti, ignition, etc. trying to troubleshoot these rolling electrical nightmares only to still not have fixed the problem. Me personally, i have done both and seem to prefer the former to the latter. Reason I say this is because if you look at the thread so far, you have had at least 3 different people with the same problem and they all have had three different responses to the fix. When mines was doing it on my camaro and fleetwood, i replaced, tps, fuel pumps, optis, plugs, wires, sensors, etc and guess what...on my camaro, it was the EGR valve, and on my fleetwood it was the fuel pump. Both cars did the exact same thing as yours. Guess who told me what was wrong both times? The chevy dealer. They hooked it to a computer, ran it for awhile, played with some things, took them about 45 minutes, and BAM!! both times they were right only after I called myself troubleshooting and spending lots of unncessary money. It was a learning experience no doubt, but not something that i will do a third time with this 96 impala. If it evens hiccups the wrong way, im spending the money taking it to the dealer. just my 2 cents!