When you get to the state where you think it should shift into OD, can you move the gear lever from OD to 3rd and see if the engine changes speed? IF so, it may be going into OD, but not locking the torque converter.

On both my vans (4liter engines and A4LD) the TC locks up at around 45-50 mph if engine is not heavily loaded. If your exhaust is loud enough, you can hear that happen as a decrease in engine speed. Otherwise, you need a tachometer to see that.

 

Bit the bullet and took it into a tranny shop today.

Tranny is hooped. First estimate $1700.

Ugh.