My 1999 F150fwd (Lariat 5.4 15k miles) intermittently seems to loose power assist when driving. I know this sounds crazy, but the steering wheel feels "jerky" and resists turning about once or twice a day. It usually happens with a warmed up engine on gentile curves at around 25-40 mph.

I've check the PS fluid - proper level, have no leaks, and no other symptoms.

Anyone ever heard ot this??? Kind of freaky.