1990 was non-HO (Renix) setup right? In the Renix setup, there are no connections between the TCM and the ECM. The TPS has dual outputs so each computer gets it's own TPS signal. The diagnostic lines on the TCM go to the big yellow connector on the passenger side instead of the ECM.
If it's an HO engine, then the TPS only has one output going to the ECM, which then relays a copy of the signal to the TCM. There is also a diagnostic connection from the ECM to the TCM. I do not know if the manual ECMs have these connections or not. It's possible the 91-96 ecms have these outputs although I doubt it. I'm pretty sure there are programming differences in the 97+ as TCM codes will trip the check engine light.