Lexus Repair: Transmission, lexus ls400, dexron iii

Question
I recently purchased a 1993 Lexus LS400 that was in very bad shape.  Slowly, I've been bringing it back to life, if you know what I mean.  I left the hardest for last.  

When I turn the car on everything works great, after driving it for a while or several miles the transmission starts to kick and it starts stalling.  Also when I'm driving on the freeway and after driving for a while and after the transmission warms up, it fails to respond.  I turn off the car and then turn it back on and it works fine.

Do you think this calls for overhaul?  What do you think is happening?  What do you recommend I do?

Thanks,

Rick

Answer
I can't really tell by your description. (No offense)
If the engine actually stalls when engaged, the torque converter is probably engauged when it shouldn't be.
Check the ECU for faults by jumping TE1 & E1 in either DIAGNOSTIC port & watching the CEL & O/D lights flash.

Alias. I would flush the transmission also. It takes Dexron-III.