I have a '72 Plymouth Duster with a 360/300hp Mopar crate engine.  I installed a CSR electric water pump and a 2950 cfm Perma-Cool electric fan, I also installed a Griffin aluminum replacement radiator.  I am having a problem with the temp creeping up when crusing.  The temperature keeps creeping up and will not stop until I shut the engine off.  I Bracket race my car and I don't have any heating problems racing, but the car only runs for short period of time.  Once I shut the engine off I can drop the temperature 40 degreess in a couple of minutes. I do not use a thermostat, I knocked the center section out of a old thermostat and use it for a restricker in the thermostat housing.  I tried using a thermostat, but no difference.  The fellows from CSR told me I was only the second person to ever call them with overheating problems with their pump.  They requested I send the pump back to them to check.  The pump flow tested fine.  They decided it might be pumping too much water too fast so they worked the impeller to cut back on flow.  It may have helped slightly, but actuall not much difference if any.  I have tried all sorts of restrickers in the upper radiator hose and also the lower.  It doesn't seem to make any difference.  I have invewsted nearly $800 and actually the engine cooled better with the factory equipment.  My reason for changing was the fact I could get a quick cool down between rounds at the drag strip, which I can. Any Suggestions?  Thanks  

The problem most likely is having no thermomstat or what you did to yours by punching the center out.  You are allowing too much coolant to pass through the radiator to allow it to cool.  Use a Mr. Gasket or Milidon 160 or 180 degree stat.  You don't really need an electric water pump either.  An aluminum after market HV mechanical water pump is good enough and with correct timing it should run cool with your good radiator and fan!

If your motor by chance is bored 0.60 thousanths over it will run hot when cruising.  Also, fresh new motors will run slightly warmer due to tight clearances and just plain driving and racing should lower this problem after time.  Even running some royal purple synthetic motor oil may reduce temp a little since synthetic oils are more slippery thus reducing some interal friction.  Hope i was helpful.

PS:  DO NOT use synthetic oil to break in a fresh motor for the first time but afterwards it is ok.  

I agree, use the synthetic oil it will help, something that is often overlooked, the transmission. Put in a high flow thermostat from summit, 160 degrees.
If you have a high stall converter it could be causing excessive heat to build in the trans. cooler, I recently added a 4 qt. B&M pan to my 360 combo with my 9 " converter. The engine temp dropped 20 degrees because the heat coming off the trans. cooler was no longer blowing hot air across the rad.
distilled water, disipates heat better than anit-freeze. you can by this water from any grocery store.  
Royal purple also sells a product called Purple ice, they claim it will lower temp by 10-20 degrees.  

You already said your old equipment worked better, so I think you know how to solve the problem. Definitly install a stat, the trans. issue is a good one, and I had a similar problem when I upgraded converters. I also had to install a 4 qt. pan to solve that issue.
I have used the purple ice, can't say it made much of a dif. also try running distilled water apparently it has a higher boiling point and will help. You can purchase this water at any grocery store.
For my street strip car I run a mr. gasket electric water pump drive at the track. I remove the clutch fan and pulley, reinstall the clutch fan with the electric pumps pulley, and it does a great job, takes less than 5 minutes, and be sure to get a different belt for the alt and run it directly to the crank pulley.
For those really hot days I have an electric fan in front of the trans. cooler and rad, but hardly ever use it.
Make sure your running an 8 qt. oil pan if you have a steep gear, that oil really can thinout on the highway. Synthetic is a great idea, I run 20w50 amsoil or royal purple.