help with 1987 full size blazer vaccum or electrical???

i have an 1987 chevy blazer k5 it is a wiring nightmare! and i have a vacuum problem, i can only get the truck to run in field service mode, when i have the aldl jumped, if i take the jumper out it dies and if at anytime i step on the brake pedal it will die? almost as if the vacuum is getting cut off. if i let off the brake pedal it will stay running. there is no leaking sound comming from booster and the pedal feels fine and the booster holds vacuum and so does the vacuum system, could it still be the booster? or could it be the 2 plugs that go into the back of the distributor?? let me know if anyone knows

The best test to see if the booster is leaking, is to kink off the vacuum hose to it and see if the engine runs better.