Crallscars

Its happened to me twice
The first time I lost brakes and steering, I pulled into a Goodyear shop, they reviewed the problem and replaced the pump and brake booster, 6 months later/ a few weeks ago I was driving down the highway took the off ramp and again no power rakes or steering, I let it sit for 30 minutes, and all was ok. The shop thinks that maybe the steering gear box is letting air into the system,

What else can it be, I am afraid to dive the truck.