RockLB

I swapped a 2007 5.3 out of a tahoe into my 79 Camaro. I used an F Body power steering pump since the truck one wouldn't work. My problem is the steering is really tough to turn. I swapped out the steering box with a reman since it was original but still the same problem. Tires on the front are 245's but I can't see that making a huge difference. Is there a different pump I should use or a way to increase pressure/flow? Any suggestions would be appreciated.