85-92 Toyota PU auto trans. shift problems

timex2timex2 Member Posts: 1
edited March 2014 in Toyota
Hello everyone, the purpose of this posting is to ask if anyone has ever had this experience with a truck, and to request any links to sites (or boards) where I might get some clues.
THE BACKGROUND
I have a 1991 4WD V6 with AUTO Transmission. It ran great for 125,000 miles and I gave it excellent care, then plooey! (It's never been off the road)
When it warms up, it shifts from first to high, (skipping second). Also, (and this is most dangerous thing about it), without any warning it shifts to NEUTRAL allowing to engine to run away and ,of course, total loss of propulsion. (This always seems to happen with an 18 wheeler behind me).
It has been in the garage or in the shop(s) for a year and I have spent thousands ($$$$). Four (4) Toyota shops and one independent later I don't have a truck.Rebuilt the Auto-Transmission. The diagnostic port shows NO failure codes, that's right, NONE! Many parts (computer, air-meter, Throttle Pos, Speed sensor etc.) have been installed, still the same old symptoms.
The hardware involved is standard Toyota stuff and they can't fix it. Given their lack of expertise I'm horrified at the thought of EVER owning a hybrid; (part electric part, engine driven).
This is not a unique problem based on what I've read on the various TOYOTA Boards on the Internet, however I never read what THE ACTUAL FIX WAS. Any of you Toyota GURUS know?
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