Tqm

I recently (two months ago) replaced my power steering gear box (bad pitman
seal and bearing) with a rebuilt unit and had no problems with steering
until today. We went wheeling up and down some hills really working the
steering back and forth and began to lose power assist. If I kept the rpm's
up it was fine, but as soon as it went back to idle power was almost 80%
lost to the steering.
I stopped several times to check fluid levels and for leaks and all was
fine. No milky bubbles or odd sounds from the pump. Belt was tight. Once
back on the road and up to speed I did notice a slight variation in assist
on the tight curves of the road. When I would turn to a certain point the
wheel would seem really easy (almost to easy) to turn for a split second and
then back to normal again. This wasn't the feeling from "death wobble" but
in the power steering feel. When I got near home it seemed to just go away
and feel normal again. I played around with it at home in the gravel at low
rpm's again and can not get it to repeat. I can't help to feel it will go
out on me again when I need it most trying to avoid trees. (Yes I did take
out the side of my nerf because of slow response steering today).
When I replaced the steering box I did the usual bleed the air out of the
system and had no trouble. Is it possible that there could have been a long
lost air bubble hiding inside the works until I gave it a good work out?
Something just doesn't seem right with it and I can't put my finger on it!
I'm going to drain the entire thing tomorrow and start from scratch, and
probably just replace the pump.
Thoughts???
Thanks
Tqm