I have a 383 stroker blueprint motor brand new has a new heater core thermostat and water pump I have drove it about 40 miles temperature gauge State about 190 degrees and did not blow out any heat through the heater and has poor circulation what that because through the water pump or a radiator
I suggest that you :
1) drain the fluid : catch it all and check the amount against what it says in the manual.
2) remove all the pipes and check for any obstructions - note a rag may have travelled further up the pipe by now - a wire "hook" can help - if it comes back with fibres on it then....
3) refit the pipes and refill the system making sure that the correct amount goes in.
4) bleed the system as per the method in the manual - some vehicles like to have their front raised , other have air bleed screws in vital places.
5) hopefully enjoy the ride as all will be ok .)