I have a 1985 K20 with a new reman 454 it seems to get very hot and goes into vapor lock. once it cools it runs like a champ. I replaced everything, from the thermostat, to the clutch fan and clutch.

Try getting an air bleed kit at the auto store. You may have a large air pocket in the cooling system. Check to see if your fan was put on the right way. I have actually seen a case where the shop somehow managed to put the fan on backwards causing an overheat condition. You can test by putting a piece of newspaper over the grill with the truck running and the hood closed. If the paper sticks to the grill then the fan is on right. If it blows the paper off the grill, it's on backwards.

Thank you I checked the fan, it was installed correctly. I will check the air pocket. I did test for carbon dioxide in the coolant, it was negative!

Sounds like low fuel pressure. 220 isn't hot enough to do this alone. Make sure your fuel likes are not running along the exhaust