OK, where do I find the PCM on this truck ?
I poured through the service manual but don't see where they show it.

 

I HAVE disconnected the battery while I was chasing a cargo light that stayed on with doors shut, but I have driven it since then and this code appears to have come from CM, so maybe I just need to disregard and it'll get forgot after 40 starts ?

 

You can hook up your test device i.e. jumper or reader. Start your test and disconnect the connector when the diagnostics start. This clears your codes. Your PCM is located near the bottom of the fire wall on the driver side. Sandy

 

Some photos from Subford:

 

Hey Sandy, thanks for the reminder ! But I kinda like the term "get forgot" ?
And SubFord, thanks for the location - looks like the same place as the one on my 1988 that replacement solved a lot of issues.

 

Same place, but.....it is removed from the engine side of the firewall.

 

OK Sandy, I started the test, and unhooked the reader. Then re-ran the tests and the 512 is gone. Back to the E4OD, Sunday, I'll pull the MLPS and check it, then change the fluid.
Buying a new-to-me truck sure kills a lot of time and money.

 

Latest update:
Since the E4OD fluid is up on the hash marks and looks light red color and doesn't smell burnt, I opted to forgo changing it for a few.
Instead, I went under there and took a look at the MLPS as I was referenced. Removing it from the mount I could see it wasn't centered on the NEUTRAL mark, just a little off.
I tested it on the bench and found that, while the resistances measured acceptable, when I set the neutral mark the way it was on the trans, it was fragile to the point that the resistance would change markedly.
So I opted to reinstall the MLPS, centered on the mark, then test drove it today.
Same conditions as last week when I had so many false neutrals, and today it performed admirably!
Hope I found the problem, with your help !

 

Sounds like you got it. Sandy