If you really wanted to get rid of the 4L80E you could get a TBI ECM from a 1988 to 1990, which had a TH400 instead of the 4L80E. Most auto parts stores can get you one, but you will have to eat the core charge on it. The 4L80E/205 combo may be as hard to find as "hens teeth", but the The TH400/205 combo is getting almost as hard to find too (being that they stoped manufacturing them more than 20-years ago).