90 max heat

I am working on a 90 maxima, the car started to overheat so I changed the thermostat and that made no difference so I changed the water pump no difference. I also flushed the rad and engine. Well I took the thermostat out and the coolant circulates good but no heat. So I went to the dealer and got another thermostat, now there's heat but very little and the gauge is showing almost at half.
Does anyone know what I should try next ? Thank you in advance.

Bleed all the air bubbles out (see manual) -and/or- drive one hour over 2k rpm with heater hose dripping....

See pages 7 &8:
http://www.cardomain.com/ride/748507/7