[fredjacksonsan]

I take it the same problems exist even after the thermostat and radiator replacement. How about the water pump? If the fins on the impeller are extremely worn, the circulation of the coolant could be reduced. (And I hesitate to mention the temperature gauge, since it seems by "one way trip" it will boil over in a couple miles)

What I'd to do check, is to start cold, with the radiator cap off. Let it idle while keeping an eye on the temperature. Once it reaches operating temp, the thermostat will open and you should see some flow across the radiator. If there is no flow, then there are 3 things I can think of why:
1) Bad impeller/water pump
2) Blockage somewhere
3) New thermostat faulty or installed backwards.

Hopefully that will help. Post more descriptions and maybe be able to help a bit more.