HO2 heaters

There are two relays in that system, one is the main power relay (PCM) which is powered on all the time and provides power to most of the engine control systems. It also sends power over the purple with blue stripe wire to the O2 sensor heater relay mounted on the strut tower. That relay is turned on/off when the Black with orange stripe wire grounds it, that is connected to the PCM at pin 14. The relay supplies power to the sensor heaters on the purple and yellow and purple and blue wires. The only connection between the relays is the purple with yellow and purple with blue (they change color at the first connection).

I don't see a second relay for the heaters in that box. Could you take a picture of it and post it? The attached is the OE diagram for that box.

No problem. Wonder if maybe they were testing the relays and swapped the high for low and tagged the high relay to track it. Or it may have come from a different vehicle. Hard to say. I've seen more than a few odd things like that. Doesn't make you stupid, just dealing with what others did before you.

I would start by adjusting the position sensor, that alone could cause the issues you have as the PCM doesn't know what gear the transmission actually is in other than what the sensor is telling it. So if the transmission is physically in say second gear but the PCM thinks it's in 3rd you get the power and shift characteristics of 2nd gear but the transmission won't act that way. Adjustment on them isn't hard but it's a bit of a mess as you need to disconnect the sensor, then use a meter to measure the resistance in the various positions. The reverse lights can help with this. Put the transmission in reverse, then adjust the switch so the lights come on and mark it, then adjust it so they go off on the other side and mark that position, now adjust the switch to the middle of that range. Then do the resistance testing on the indicated pins. If it's in range and works test it on the road.
If it still isn't correct then please ask a new question relating to the transmission and include the testing results and symptoms.

Do the reverse lights engage when in reverse now? If not it's possible there is an issue with the resistance readings at the PCM itself. That is what the PCM uses to adjust the shift points and characteristics. If the trans fluid was recently changed it shouldn't be the issue. However it could be internal to the transmission as it sounds like it's heat related. The solenoids can be affected by heat as well.

Okay, if it sat for that long it's likely that the seals and transmission parts are sticky or actually dried out. For that I would try adding some Lucas transmission fix additive. It should help bring the seals back to life. If possible run it some to get the transmission warmed up and circulate the fluid and add the Lucas. Then run it a bit more and see if it comes back. I've had good luck with it in vehicles that have sat a while.

It can take a while as it has to actually work on the parts chemically. After setting that long the end result may be that the transmission will need to be rebuilt. I doubt it's any electronic issue unless the PCM has an internal issue or the passages in the transmission itself are gummed up and blocking flow to/from a solenoid. It's why I tell people that leaving a vehicle setting for a long period will do far more damage than driving it. I have an older Blazer that has been setting for a while, it's currently waiting for spring to be stripped down and rebuilt using some "better" parts. While it has been setting the injectors have stuck, the brake master has failed and the transmission will barely shift and it ran like a watch before it was parked.

Nope. No mention of that. Whose wiring diagrams did you use? OE or other? I guess it would be possible for it to be improper in that case.

That should cover it. I just wondered if you used only one source as some of the non-OE have been known to have errors in them.

Keep working on it and you'll be able to take it to the track. LOL