My Firebird Formula will not start. Fresh rebuilt engine, new Battery, new starter. What is the DEAL!!!?

I have a 1975 Pontiac Formula. The starter is making a very very slow slow turn. At first start it jumps but no crank. Then it goes like no battery left, however the battery is good, I have even had it jumped by another vehicle while trying to do this. I had the engine rebuilt (Pontiac Big Block 400) I have a new starter and new battery. I have gone through all the cables leading to everything, the ground from the batt to the block, the ground from the block to the chassis, positive from the battery to the starter, ignition cable to the starter, I even added a negative from the starter directly to the battery. Everything is brand new on the motor. New distributor, new carb, new gears, new fuel-oil-water pump. Everything was torqued on to factory specs, cause I did it myself. However I am getting a very very slow crank out of the starter. I have replaced the starter 3 times, thinking that it may be a faulty product, but still acts like the battery is dieing. What is my problem? Help me!
My Firebird Formula will not start. Fresh rebuilt engine, new Battery, new starter. What is the DEAL!!!?
This is just a guess Todd. When you took the original starter off was there a shim between the starter housing and the bell housing it bolts too? Do the specs call for a measured distance between the starter gear and the flywheel teeth?





When you "went through" the cables I assume you measured the amount of resistance in the cables in ohms? Could the wire from the ignition (purple?) that goes to the starter have gotten broken due to it's age?





Hope this helps