My 2001 5r55e took exactly 4.5 qts of Mercon V after a pan drop and filter change. It was full when I drained it and I just measured what came out and put the same amount back in.
BTW - I used the rubber composition gasket that came with my Wix trans filter. I greased it lightly, as the directions suggested, and snugged it down with a 1/4" ratchet. It hasn't leaked a drop in 4 years. You should use a torque wrench and torque to spec. The reason sheet metal pans leak is because people over-tighten them. Once a pan (or valve cover) is over-tightened you will have leaks.