Hesitation problem I cant fix

Vehicle:
· 1993 Oldsmobile Cutlass Ciera 81,000 miles

Specks:
· Engine: 3.3L 6 cylinder (AKA 3300)
· Transmission: FWD transaxle 4 speed auto 440-T4 (AC Delco fairly new)
· Fuel used: 87 octane

Symptoms:
· Vehicle hesitates/stumbles under load after TCC lockup in 4th gear (overdrive). Problem only occurs with slight acceleration between 55 – 75 MPH. If gas pedal is stepped on harder vehicle will kick down a gear and operate fine. Vehicle will also return to normal operation if brake is tapped (releasing TCC lockup).
· Vehicle will occasionally surge upon hard acceleration from a stop.
· On a rare occasion vehicle will “reverse backfire” upon hard acceleration from a stop.
· If radio is on with volume all the way down you can hear a whistling noise through the speakers that synchronizes with acceleration & deceleration.

Codes retrieved:
· 28 – 3rd gear switch
· 39 – TCC circuit

Actions taken:
· Replaced spark plugs
· Replaced spark plug wires.
· Replaced air filter
· Replaced all 3 coil packs
· Replaced O2 sensor
· Replaced all vacuum hoses
· Replaced both brake switches (one of which controls TCC unlock)
· Cleaned mass air flow (MAF) sensor and housing (made vehicle run better but did not fix targeted problem)
· Replaced TCC solenoid (6 hour job)
· High pressure “on the car” fuel injector cleaning
· Replaced fuel filter
· Tested battery and alternator
· Tested throttle position sensor
· Killed 3 chickens & a pig, drank their blood, and prayed to the GM Gods

My thoughts:
· I believe the codes 28 & 39 are false codes
· The freeway speed stumble feels like an ignition problem to me but I could be wrong
· High octane gas seems to reduce the problem
· From stop surging/”reverse backfire” is almost non-existent since listed work has been done but felt like an emission problem

As far as the surging is concerned from stop to drive, I would remove and clean the IAC (Idle Air Control solenoid) with a throttle body cleaner and a brush. Clean also the spot where the IAC goes in. If that does not fix it, it might be time to replace the IAC since IAC goes bad over time.

You might have a dead spot on the TPS (Throttle Position Sensor) at higher speed. The TPS can't be cleaned, you just have to replace the TPS itself.