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The box the TCM is in is not know for it great ability to keep out moisture/water

Yes, you should make sure the problem is not between J1 and the TCM. Actually by now you should have checked/re-seated those connectors.

The TCM probably does not monitor the 5V reference output for a TCM bad indicator

If you are getting 12V to pin J and C on the cannon plug and ground is good to wire 599 then the 5v reference in the TCM is Kaput This would also explain the problem you are seeing on the engine speed sensor as the same 5V reference is used for the TPS, ESS and TTS (trans temp)

If you get all the way back to C4 and still no voltage the TCM is bad.:cry:

Yes one should be 5V There may be connections in between that plug and the TCM box because the wire at the TPS is marked C and at the TCM connctor is marked A so the next step would be to back up to the TCM box connector and see if you have 5V on pin d, wire 350A, if you do then start looking...

Looks like you are routing out all the problems!!

It is a little easier to read if you rotate it correctly.

That does not jive with the documentation I gave you.

Can you tell me what page the voltage is listed on, I can't find it at first glance.

How many ohms does the speed sensor test to (disconnected)? are you using AC or DC scales, you do not have a code 71 so I am curious why you are looking at it.

I am a little confused, what does RPM have to do with the TPS? So wire 350C, terminal A has 5v measured to ground? and wire 350H terminal C measures near zero OHMs to ground? And you have no voltage on wire 350B terminal B to ground? All this is measured with the plug connected to the TPS...

Only one TPS, it would be the easiest to diagnose first, just go after them one at a time. however it is doubtful the TPS alone caused all the codes you are seeing but a defective or badly miss aligned TPS can cause "soft shifts" that could be mistaken for slipping. The 85,86,87 codes are an...

I don't think that TCM ever had a OBDII port, it had an OBD port which became known as the OBDI port when the OBDII port came out. The OBD port on that TCM has a very limited amount of information, that is why it is mainly diagnosed using the codes and a pressure gauge. The last transmission I...

If you live in a fairly large town/city check with the local hot rod guys, the 4L80 is a popular hot rod transmission and shops they deal with would be more likely to welcome you, many shops rather just deal with soccer moms etc.

It also would not be a bad idea to drop the pan and change the filter and look at the pan, if there is a significant pile of clutch material in the pan then it is pretty much game over, a small amount of "sludge" is normal, metallic flakes not so normal. This is a BAD transmission!!

It needs to be diagnosed, you could have sensor failures and slipping and going in and out of limp mode sometimes is caused buy a solenoid/valve failure, both relatively easy to repair. It is best to have someone familiar with the 4L80 to do the pressure testing, they know what the pressures...

The mechanical side is the same as a civy transmission, they should be able to do basic troubleshooting such as putting a pressure gauge etc. The electrical side will likely be foreign to them, all the basic controls are the same but there is no civy port (OBD) to read the TCM but that...

It is normal for it to read high when off as the torque converter sometimes drains back into the pan.

In case you don't have this, if you think it is slipping the first step would be put a pressure gauge on it.