ELECTRICAL
Powertrain Control System - Refer to engine Section to diagnose erratic engine operations. Basically, first step is the make sure the engine is in good condition. electrically speaking, this would include all sensors, coil, plugs and wires. Yes, it is possible that when you cleaned the engine that you could have damaged a sensor on either the engine or transmission.
Engine concerns - Perform Shift Point Test. Refer to Road Testing the Vehicle procedure in this Section. You have pretty much done this and provided us with that information.
Electrical inputs/outputs, vehicle harnesses, powertrain control module, shift solenoids, transmission range sensor, stoplamp switch, TCC solenoid, vehicle speed sensor, throttle position sensor, TSS, EPC, 3 - 2T/CCS - Basically at this point they want you to test all these aspects of the car. You can't do that without a very in-depth scan tool, so... Plus, most problems with any of these would throw a CEL anyway.
HYDRAULIC/MECHANICAL
- Improper Fluid level or Condition
- Speedometer drive gear damaged
- Speedometer gear damaged
- 3-2 timing valve, pull-in valve, 2-4 accumulator, servo release shuttle valve, 3-2 control valve stuck, damaged, misassembled
- Solenoid screen blocked
- Separator plates damaged, blocked
- Pressure tap plate/gasket damaged
- SSA, SSB, 3 - 2T/CCS Solenoid not functioning properly, stuck, damaged
It could be any combination of these things. so, as you can see, it could be a daunting task to narrow it down properly without just telling you to start throwing parts at it. I also looked into the problems you were having with slipping when you would engage 4th and most of it is the same as above, but also encludes things such things as slipping bands, leaking or damaged servo... the list goes on.
The fluid that you got, as long as it was a DexronIII/Mercon approved fluid you should be ok. If not, then might be the reason for your more recent problems.
