[Speedbumpauto]

If you have one of the chrome overflow tanks, it probably doesn't hold enough for the capacity of the radiator in an iffy situation. You don't have to get on the road to test it. Let it run in the driveway until the fan comes on then check the gauge. The upper hose should be hot. That means the T stat opened and circulation is happening. THEN shut it off, let it cool some and open the cap, carefully, and check the coolant level in the rad. MANY times an air bubble will have burped out when the T stat opened and the level will be low. Top it off until completely full and put the cap on and start with an empty overflow tank. Drive until temp above 180 is reached. Take it back home, shut it off and wait about 5 minutes for heat soak. Then check the overflow tank.(not the radiator!) If it is not full, you can add a little for safety as what's in the tank when hot is the amount of coolant expansion you have in your system. When the truck is completely cool. Recheck the overflow. The level should have gone down to where there is only a small amount in the tank. If you have some amount in when cold and a high, but not puking out, level when hot, that is the static level your system wants. The small, cute overflow tanks can make you be very precise. On most of them you can add about 3 inches of 1/4 fuel line to the top of the tall tube inside the cap without interfering with the cap. That gives you more coolant when hot without puking it out. Sometimes that small amount will make the difference. If none of this works and it still gets hot, we need to have a discussion about good radiators and cheap radiators. I had the one for my T roadster made by a guy in north Phoenix that does street rod radiators. It cost $600, but it works now, along with getting the larger chrome overflow tank and the other things I talked about. Lots of guys here may not know about AZ summers, I do and have had the kind of problems you're having with hot rods and engine swap vehicles.