7.5 water pump issues

[Wingedwheel]

I have a 1984 7.5 merc. I replaced a coil to get it running and I noticed it was not pumping water. I removed the lower unit, saw the impellor was old and brittle, replaced it and still no water. I blew air through all the lines and they are clear. I took the lower unit and manually spun it with a drill in a tank. It was pumping some, but in my mind it looked weak. How much pressure should the pump put out? I don't think theres enough pressure for it to make it up to the powerhead. The stainless plate in the pump housing looks good with no scoring. I'm getting frustrated..... Any ideas?