Kipparham,
Putting the leak aside, the problem you discribe with the pedal could be due to the brake shoes needing adjustment. If the shoes are to far away from the drum it takes more fluid to get them to make contact than you get with one pump. Along those same lines of thinking, if the Master Cylindar bore is to small you can't push enough fluid in one pump either.
If I remember correctly the 1-1/2 & 2 ton Chevy trucks use a MC with a 1-1/4" bore.
Hope this helps,
Mike B
