This is the problem I’m having with my 2006 Ford f150 5.4.as long as we are accelerating it’s fine runs perfect, when we go to turn and brake, power steering goes out and it tries to shut off, so I have to throw it in neutral and tap the gas then back in drive and hurry and press the gas for it to not shut off.
I’ve already replaced the variable timing controller on it, then replaced the camshaft sensor, it threw those codes so I replaced them, now the only codes it’s throwing is the o2 sensors because cats are cut.m, and there is no o2s. It runs perfect in park, stays at the rpm’s it’s suppose to and will run everything, my 2 amps and subs.

 

I can't think of anything that would cause the power steering to quit working except a loose/slipping belt, so I'd check that first.

 

Have you checked the power steering pressure switch located on the power steering line? If the power steering pressure switch is faulty, it can cause the engine to slow down, stall, or speed up and then slow down. It can also cause the check engine light to come on.