727 problem

[1965ply]

driving veh for about 30 minute on the highway at 55mph trans started to smoke, pulled over and transmission pan gasket blew out and all oil leaked out. seams like there was a lot of pressure in trans does anybody have any idea what could cause this, gasket was changed about 2 weeks ago it shifted ok really no indication for gasket to blow out, transmission was stock it a 1966

 

[Hemi Rebel]

The only thing it could be is the vent is clogged. Its odd it blew the pan gasket and not the tail shaft seal or pump seal.