OK, while I had my truck the lift to re-bush the front end, I took a look at my transmission's electrical connections. Both of the connectors are three-pin connectors! So apparently, I have a 47RH. That would explain it acting like it has a lockup convertor and why it wouldn't release on its first trip. 600 miles of it stalling at lights, and then all of the sudden it behaved like a normal 518.
Now the big questions are:
What's controlling lockup?
Why is it not locking up?
Why did it lock up but not release?
And did I burn up my lockup clutch on my first trip?
While I'm asking, where is the test port on the tranny?

 

if they have the lock up wired wrong it will be locked up all the time, OR if there is trash infront of the lu solenoid it will lock it up and keep it locked, the clutch in the converter is really small and to put all the torque on it takes them out really easy. as for the test port i'll have to see if i have the picture.

 

Thanks! Tomorrow morning I'm going to wire a switch from the rearmost wire to ground and see if I can actuate the lockup. I have no idea how or whether the previous owner had it wired for lockup. All he told me was he had the transmission rebuilt. I was quite surprised to find 3 wires coming from what I assumed was a 518. If it tries to lockup and slips, I guess I'll be investing in a Goehrend TC.
I'm ASSUMING that I'll hear a click when I flip the switch to actuate the lockup solenoid....

 

probably won't hear anything (haven't really listend) because its on the valve body sitting in fluid so unless its really quite and you have really really good hearing you probably won't hear it. I don't have the picture on this computer and the other one is down right at the moment, someone else will probably chime in.

 

Well anyway, I should feel SOMETHING when I engage the lockup clutch even if it's toast!

 

According to the ATSG overhaul manual...

No 4-3 downshift could be...
-faulty lockup solenoid, not venting
-valvebody malfunction
-faulty wiring
-faulty ECM

 

I had no problem with downshifting. My problem was TC binding and feeling exactly like a lockup clutch not releasing. Strange, considering my TC has no lockup clutch! Goehrend told me their theory section on their website explains it, but I've read their theory section over and over and found no explanation!