Is it the waterpump?

[Oldgearz]

Ok so I was tinkering w/my guages since they don't work. I took the cluster apart, cleaned everything up and put back together, now fuel guage works, but coolant temp was still showing C when truck was running. I then troubleshot the problem, cleaned all grounds that I had access to, then went to Pep Boys, got a new sending unit for a 66 (all that was in stock). I hooked it up, ran the truck, now showing right below H when warmed up and running around a little bit. So I figured the thermostat was maybe stuck closed. I removed it put it back together, ran the truck around a bit and it was going right back up to the H. Is it the waterpump? I did notice my coolant looks like crap now that I removed the thermostat. Truck runs fine, the newly rebuilt radiator is hot but barely any hiss at all when I loosen the new radiator cap. Can this be just a bad ground or is my waterpump shot?