how much can a 400 tranny handle

i brought my motor home back this weekend its a old 74 fleury with a 12,000 lb gvw with a 454 with a oil cooler and a deep pan 400 tranny. the unit has a big rad internal tranny cooler and also 2 aftermarket tranny coolers set underneath the front bumper in the air flow. i suspect the previous owner had a tranny loss and made darned shure that he would not have it happen again.
i am courious how big a units they put these trannys in, i know that they are tough but how much abuse will they take ? within reason.
i drove it about 180 miles into a pretty stiff wind today approx 80 deg to get it home and went under after and felt the trany pan too see if really hot and it was not bad, i assume the aftermarket coolers keep it within reason.

Heat is an automatic's worst enemy, so the coolers are the way to go. If a 400 won't hack it, you're out of options other than a truck tranny like an Allison or a stick. The 400 is GM's best auto.