I would take each wheel cylinder and caliper apart. Two years is a long time to sit. Get some rebuild kits and go to town redoing your cylinders. Ensure you bleed the line completely, get a few bottles of brake fluid.
If after all that is done and still same problem, go back to the parts truck and get a proportioning valve and replace your old one. Re bleed all your brake lines again.
Do you have power brakes? Is your booster working correctly when motor is running?
just a few thoughts. SgtDel
aka "Andy"
www.delbridge.net
1979 Big 10 383 stroker
1991 Blu 'Burb 3/4 ton 4x4
Sounds like the booster you put on is worse than the one you replaced. They don't cost much new. I think I paid about $100 for the booster AND new master cylinder from Autozone. - Mr Diesel
'76 C30 Crew 6.2