Bobwolverine

I have a 1979 Chevy K10 4 wheel drive with a TH-350 trans. I had it parked for about a month because i couldn't afford the gas to drive it. I went to start it up and checked the trans fluid and the dipstick was dry. I went to the store and got 4 quarts of fluid and attempted filled it up while idling and checked it between bottles of fluid. The dipstick was still dry after 3 quarts. i put one more quart in and it started pumping fluid out of the vent hole. Any idea why it would be doing this. I have heard that if a TH-350 sits with out being drove for too long the torque converter will bleed back into the trans but i would think it would just read over filled on the dipstick. Any help would be great.