Loosing speed going uphill and revs at 3500 rpm+

If it was fuel filter, I don't think he'd be pulling 4000 rpms with his foot to the floor?? Clogged fuel filter would not let it rev that high as far as I know.

Probably normal, and he just does not expect that kind of performance loss going up the grades?

Not that it makes any difference, but what chassis is it? (Ford or Chevy).

Good luck!

Mitch