Forgot to post my towing experiment. I had to drive northeast about an hour from my place with my trailer and pick up my son's car. He hit one of these in the middle of the highway;
His Miata actually weighs about what my mustang does. We loaded it up and drove home and my tranny did not get hot. I think my problem is finally solved.
Just to jog anybody's memory;
had the trans rebuilt with stiffer shifts, some stall, heavy duty rebuild kit
put an external cooler on it
3.25 rear end gears
I think the lower rear end gear did a lot of good. It had something like 2.75 or the highest gear you could put in the thing.

His Miata actually weighs about what my mustang does. We loaded it up and drove home and my tranny did not get hot. I think my problem is finally solved.
Just to jog anybody's memory;
had the trans rebuilt with stiffer shifts, some stall, heavy duty rebuild kit
put an external cooler on it
3.25 rear end gears
I think the lower rear end gear did a lot of good. It had something like 2.75 or the highest gear you could put in the thing.