8 3/4 Vent Blow-By

The only time I've had that happen to me was on a 71 Dodge PU with a 8 3/4 and it was because of excessive heat do to a bad wheel bearing. I think you need to take it apart and see what is causing the heat build up. Also by what your saying that it only happens when it is 80-up degrees in the day, this is adding to the heat generated by a bad bearing.