Pull your plugs. Make sure it's not a head gasket issue. That was the problem I had with the hot rod. You can usually find it by a loss of coolant.
My lower hose was being sucked flat at a bend where I couldn't feel it. If your hose has a good spring in it that should not be your problem.
There's always the thermostat and radiator to look at.

Since your pump is out pull the block drains and flush the block through the water pump holes. That will make sure you don't have a heavy layer of ickies in the block. I also had that problem but never knew it because the coolant wasn't nasty looking. The sediment simply didn't get stirred up.