maybe another solution
i have a 355 tpi in my blazer had the same problem at the beginning, three chips no good , the last one was ok but the check engine light was on all the time but no code . i got accel dfi it was easy installation and 1 hr of tuning at a accel licensed shop. think about it $200-300 for every chip on the chevy ecm or 1 hr at a good dyno shop every you want to modify your engine. just my 2 cents o yea the accel runs like a bat outta hell