Transmission fluid leak

I have a 94 Astro 4.3L Vortec. Recently, there has been a transmission fluid leak, but only at high speeds (80+ km/h) (50+ mph), or when going up a hill. Small droplets of oil appear on the back window. There is also a cloud of blue smoke behind the van and the smell of burning oil, probably from the oil hitting the catalitic coverter. We have changed the seal between the motor and the transmission, but we still have the same problem.

Also, after removing the engine cover, I noticed that the hose for filling the engine oil has come loose. I am wondering if this could be a problem and how do you get it back in place. The hose still goes into the engine, but the rubber seal is not in place.

Any help would be apreciated.

Are you sure it's tranny fluid?
I'm thinking that maybe you have a high-mileage engine, and the blow-by is pushing engine oil out thru the disconnected oil filler.
You get more blow-by under load.
Which is loosing more oil? engine or tranny?