1995 GMC Jimmy Truck starts, then quits

Hi, my Jimmy is starting ok, but shortly after it just quits, a short while as you are driving. No lights or info. Appears to help diagnois the problem. But as you loose vacumme you have hard to- no brakes or steering until you come to a stop.

Of course when you are driving down the road, that's not good.

You can then start the truck back up and while I only dared test this a few more miles, it did remain started. So I parked it. A parked car does me no good, lol.

Any thoughts as to where to look for the problem?

Thank you

PS: It has a new fuel pump, battery, all brakes, drums, rotors in short $2,600 of repairs, and now this problem. (Insert very sad face)