Choking in D gearbox related ?

Hi over there.

My 79 LeBaron with a 904 + overdrive has a problem accelerating when warm and in D. It can crawl along in a little over idle speed, but it dies when I try to accelerate any harder. There are no problems revving in P.
All the lean-burn stuff has been removed and replaced with a conventional electronic ignition, and the carb has just been replaced with a new Carter BBD.
The car is right now with my mechanic, who has looked around on the web, and found that maybe the fault...

Choking in D gearbox related ?
Author: Toro67