94 Olds 88 - 3.8L - Coolant fans won't shut off

With a stone-cold engine, I turn the switch to ignition, and after a very brief delay, both coolant fans come on, low speed. After another very brief delay, the larger (driver's side) fan goes into high speed. The fans never cut off, but continue to run non-stop in high speed even after engine is warmed up. I've got coolant fan schematics from AllDataDIY and have eliminated the engine coolant temperature sensor that feeds the PCM (correct ohm's at sensor for engine temperature per chart and correct voltage across sensor (5V). I have also eliminated the A/C Pressure Fan Switch that feeds the PCM. It's open with A/C off and has correct voltage across switch (5V). Those two sensors/switches are the only ones I believe have the opportunity to energize the low and high speed coolant fan relays under the hood. I've also swapped the low and high speed coolant fan relays around since they have identical GM part numbers, with no change. It's beginning to point to the PCM, but I really hate to lay out a couple of hundred $$ if there's something else (simple?) I may have missed. Any input would greatly be appreciated!