Have you figured it out yet? Your mods look good but everything points to a lube problem. You said you blew the cooler out and it was good. What I realized sometime back is that air pressure is not the same as lube pressure. I've been able to blow air thru coolers before that wouldn't hardly move any fluid at all. With the tranny back in the car ,leave the back cooler line off and run the line into a bucket and start the car in neutral , you can actually watch your flow and time it. The older Chrysler service manuals says you should be able to pump at least a quart in 20 seconds. I'm just saying don't trust the air pressure method when checking or flushing a cooler.