Big smoke: is my engine sucking auto trans fluid?

[GGR]

The other day I made a 400 miles trip with my heavily loaded 3.5. I noted that when I was pressing on the gas pedal to keep my speed while driving up hill on a mountainous highway I had a big whitish smoke after a certain point. Smoke disappeared when I was easing on the gas pedal. I first thought I blew a head gasket but coolant liquid is fine as well as engine oil. Only the transmission started being noisier and it was missing between one third and half of a quart when I checked the level. Is it possible for my engine to suck auto trans fluid? If yes, is it an easy fix? How do I do that?

Thanks!