Why did you replace the water pump and T-Stat?
Being a Renix, closed coolant system, One high probability is that the top half of the radiator has air trapped in it. There is one easy trick to filling it, pull loose the driver's side heater hose at the T-Stat, it by passes the T-stat and lets air out of the block, then fill the coolant bottle till the block overflows. Then try again. It is the only easy way I know of that is fool proof for getting the radiator filled. Test the top and bottom of the radiator as it heats up to see if the top is as hot as the bottom.
You may have other problems, like a clogged radiator or....so we need more input.