On the 3rd trans pan and!

[Nickelcharlie]

I have a 86 GMC pickup with a 350 auto and I am leaking transmission fluid while driving.
I am on my third transmission pan trying to stop a fluid leak. It leaked on the original pan, a chrome one, and now a thicker aluminum pan. Today I started driving to a car show and it started fogging smoke out from underneath the back of the truck. This time I used a thirty dollar gasket between the trans and the pan! You know the thought, the more it cost the better it should be!
I am thinking there must be some pressure build up causing the fluid to be pushed by the gasket!
Any suggestions what to look for would be greatly appreciated!