About a week ago i lost power steering in my 2001 F-250 5.4 plow truck. I lost it last thursday and went to drive it to my garage friday to put on the new pump, I had powersteering. I have gone a week plowing and haven't had any trouble until today i lost it again. When i lost it before i could still have powersteering when i revved the truck up. That is why i thought it was the pump not flowing enough at low RPMs but now i don't have it no matter what RPM. Yes it is full of flud (lucas actually). Do you guys think something is freezing up (water in the pump/lines), or its the steerint gear or pump??

Thanks guys.

again its a plow truck so i need to get this thing solved. I live in Erie pa.