Truck dies...IN EVERY GEAR!!

It just started doing this yesterday out of the blue. The transmission shifts fine but has no kickdown at the moment but that hasn't given me any trouble at all. It been having an issue with the brake booster lately that it will kill the engine when you stop or even if you are in park and just slam the brakes, but now, it just dies whenever you are sitting still, even if its in park!! Unless its stone cold, it won't run for long in park. It'll stay running in neutral or park if I give it a lil gas and hold it to keep it alive.

Please guys, anyone know what is causing this? Could it be a vacuum leak?

whatever you do, get that fixed and set-up immediately. this will burn up your trans. if anything , at least tie it halfway back.