why is my truck running at 300f

Too lean, richen up the high speed needle. You should be able to see exhaust when you are running, also running in long grass tends to elevate temps.
HTH
Rod

Let out of the throttle every now and then.

Since you have savagex24 as a username I take it that you have a HPI Savage? Must new people usually think that it is always the HSN that makes you engine run to hot but it usually is the LSN. What are you current needle settings? What temp is it at idle? How much fuel has been in it? It also could be an air leak. Is your fuel line ok? Fuel filter? Have you put gasket goo around the backplate/carby/needles?

Cheers

How long is a peice of string? We need more info!!

For starters, how about telling us what engine, fuel, plug you're using. Is the truck brand new? If so, have you run the engine in? Is the carb at the factory settings? What's the weather like?

It sounds like the main mixture is too lean. If it is, you can richen the LSN all you like and it won't make any difference. Since adjustments to the main needle effect the fuel flow through the LSN, always adjust the main needle first, get it in the right ball park, and then you can make small adjustments to the LSN to ensure smooth throttling.

Air leaks can cause over-heating, that's for sure. In addition to what's already been listed by Inferno, common causes of air leaks are:

loose screws on the backplate
loose screws on the cylinder head
loose pinch screw on the carb
loose main needle banjo fitting
broken/poor fitting/perished tank lid seal o-ring