Okay I had to think about this. I bought the GM updated Prom, code ABYK, from P & G Chevy. I had the 1990 OEM PROM. I looked after reading the TSB over at the Reg site & my symptoms matched so I put it down on my list. I know the shift light worked before I swapped PROM's and I know that after I did my plenum stuff I put in the GM/ABYK coded PROM and the shift light still works.
btw, Bob it sure does sound nice...sweet music you're car's making! You must be
Tom