The ideal way to solve this would be to go into the program and delete the transmission code. The trouble with this is that there is very little software support for the series I ECM's but you may find it online Replacing the shift solenoid inputs with bulbs should trick the ECM into believing that the solenoids exist . I just don't see this as the ideal solution.
Ryans trick about sending a message to the ECM that the transmission is in drive is a unique solution but I am not certain how that might affect other ECM operation. It may very well work but having never tried it I just don't know. Perhaps Ryan has had overall good results doing it this way.
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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE " [This message has been edited by Dennis LaGrua (edited 02-25-2022).]