1999 Ford F-350 Powersteering

I do not think that one could affect the other.

To check if a brake booster has failed, do the following;

Before starting the truck, pump the brake pedal till it is firm.
Next, keep your foot firmly pressed down on the brake and start your truck.
If the brake booster is OK, it will fall away under your foot and not be as firm.
Sounds wierd, but true.

The brake bosster uses vacuum to assist in decreasing the amount off pedal pressure it takes to stop the truck, thusly the drop in the pedal when starting your truck.
Some trucks do use air brakes and some off roaders even use hydrulically pressurized systems that us a pump just like a power steering pump. You can look at the bosster on your truck and see a vacuum line, about 1/2 in diameter or less, that leads to the manifold or some vacuum source.

If you are running big tires or carry heavy loads, power steering racks and pumps can wear out more quickly from the extra stress.

Check the power steering fluid.
Is it burnt or a dirty brown color?
Does it smell burnt?

Let me know how things go and I will check back to see what the fluid is looking like.

If your experiencing steering issues, it is probably the pump or rack. I will help all I can to get it figured out.

Okay, I have heard of these. One pump to pressurize steering and brakes.

Since the question was asked if they can affect each other, Ford Tech has answered that. There must be some problem that you have noticed with the brakes and steering that started at the same time.

Check the Hydro fluid, does it look or smeel burnt?
Look for luid leaks around the system. Lucas Power Steering stopleak is a good quick fix.

Do you hear any squealing noises coming from under the hood around the time the issue started?

What kind of problems are you experiencing?

Yeah, sounds like the hydroboost needs to be replaced.
The squealing and leaks are a sure sign.

Let me know how it goes.