Weird cooling problem

[KenC]

I've been having some trouble with my cooling system and I'm not sure what to attribute it to.

I replaced the block recently and subsequently replaced all of the coolant.

My thermostat has about 5k miles on it, and the water pump has about 300 miles on it.

I have properly bled the system three times (waiting for the thermostat to open and the bleeding on an incline).

My problem:
During extended amounts of driving (over 20 minutes), the temperature gauge begins to creep up to the mid mark and exceeds it by a minute amount.  This is above the normal operating temperature.
I also find it strange that my heater temperature (blower heat) varies greatly upon the rpms of the engine.  I understand that due to the increased velocity of the coolant flow when the water pump is moving faster that the temperature may increase slightly, however, if I drive above 3,000rpms for more than 30 seconds, the heat becomes unbearable (it becomes painful to hold my hand in front of the vent).  If I drive at low rpms or idle, the heater temperature decreases.

Does any one have any idea what could be causing this?

[RED IS 91]

My needle is a whisker above half . This is normal .

[quinn11m20]

Mine does the same thing to.

[KenC]

My needle is a whisker above half . This is normal .

Well regardless of where the needle is, the cooling system isn't working properly.