2Blade,
Get ahold of a copy of Rick McKinney's book "The Simple Art of Winning" - it has good diagrams and discussion on proper back tension and which muscles are involved.
First of all, you shouldn't be really "pushing" with your bow arm. You want to lock the humerus in the socket and let it stay there...continuing to pull with your drawing arm. Yes, you've got to initially do some pulling with your bicep and triceps on the drawing arm, but once you get the string on back towards your face, the upper back muscles (traps, lats, serratus) take over and the forearm and upper arm should become a big "hook" on the string.
Don't try to squeeze both shoulder blades together, but instead try to pull your drawing arm shoulder towards center. Have a good grip with the bowarm, but kinda let it relax, seated firmly in the socket.