No heaters and bad circulation.. help please

[ZANDER]

Know that this is a a common thread, but interested in your views in my situation..First of all there is no heat if driving on a cold day, very small amount of heat if day if not cold...
My first steps were
I removed the 2 pipes that go to and from the heater rad, water very rusty colour... hooked up garden hose and ran water through the heater rad so its not blocked,
i also tried this with temp dial at hot and then turned to cold... water passed through when heater set to hot and stopd when turned to cold.. so that valve is working...
one thing i noticed when i took off heater pipes was that there was little or no flow until you revd car up...and i think heaters get better if you sit in on spot and hold her at 4 or 5k revs..and heaters seem to die again when revs die down..
Top tank of rad was very hot, core of rad was cold.. bottom pipe cold and top pipe roasting but when i pulled top pipe off had nothing in it...
all the above were pushing me and anyone i asked to conclude water pump with fins broke off.. so i purchased and went to the hard job of fitting it today... bad news is the old pump looks fine and thermostat is opening and closing in boiling water aswell... fitted the new pump anyway but havent her running yet as the Anydarkness caught up on me tis eve...Temp gauge always stays around half way and ive never heard gurgling from behind dash??
i am puzzled now, was sure the pump wasnt pushing the water around
help appreciated