it started leaking and whining

should i replace both you thing or just pump?both are under lifetime warranties

The old pump might have put some metal or junk through the system. Or might be a bad hydroboost.

Do you get zero steering assist until 1,000RPM?

maybe a little at most but after 1000 its back to normal.and brakes work no matter the rpm

The boost may be more likely than the pump but without doing testing we are just guessing.

might try i good flush before i go changing anything.got any idea how much fluid it might take?and being gm i should use power steering fluid like the it recommends and not atf?

Yeah, use power steering fluid.

Here'* a good way to test: Buy the world'* least-expensive power-steering pressure hose for a non-hydroboost version of your truck and hook it up (bypassing the hydroboost). See if it steers like normal. If so, you have identified the hydroboost (or the hoses but unlikely) as the issue.

just installed a new pump and it fixed everything.thank you guys for all the help

Thanks for letting us know how it came out.

Curious: What brand was the old one?

With all the high quality (sarcasm) units on the market, I'll guess Cardone, aka Car Done.