86 toyota 4x4 (22R) Gradual Overheating

My 86 Toyota 4x4 pickup with 22R motor gadually started to run warmer than usual and now it goes directly to just below the red line as soon as I start it. I haven't run it to the point where it everheats yet. I changed the thermostate, radiator, flushed and backflushed the system with no luck. The pump isn't leaking and the fan and belt look good, however, the coolent is not flowing properly and the heater blows cold air. What should I do next, replace the heater valve, heater core and/or water pump? Any help would be most appreciated.

AndyB

A worn impeller on a water pump will restrict the flow of coolant. Worn out water pumps do not always leak. Do you know how old the water pump is? Did you flush the heater core separately from the rest of the cooling system? Make sure the heater valve opens and closes when you operate the control. Make sure the thermostat is working at the correct temp. To check it, you put it in a pan of water on the stove and heat the water. You then measure the temperature of the water when the thermostat opened.