John, I wouldn't worry about the drill motor's speed. I've seen over 25# of pressure on a gauge and
oil in the valve train using a quarter inch speed handle and socket, and just about any drill should do better than that. This is only me, but I'd be tearing the thing down checking bearings, galley plugs, etc. Like we in the south say; Sumpm ain't rite! Steve
P.S. come to think about it, why don't you try the 1/4" speed handle and socket thing, if you don't feel much resistance try another pump. Just an idea.