I've been having some overheating problems on hills and at higher highway speeds. Tstat has been replaced and I've been told its probably my radiator...plugged up in the bottom.

Instead of buying a brand new one can I just grab one out of a salvage Toyota truck or 4runner? I'd only do that if it was new enough to still be ok...i realize grabbing another 21 year old one probably wouldn't be a great idea.

 

A used one is a gamble. It may or may not solve the problem.
Out of curiousity, you've purged the air out of the system, checked your water pump and have your timing set properly?
How many miles are on the engine? Does turning the heater on help keep it cool?

 

There's 140k on the engine.
The air was purged recently...but I was told that air pockets wouldn't cause that kind of a overheating problem.
It will cool down if I just let it idle...and it helps a lot if the interior heat is on full.

I can check the water pump just by looking at flow thru the radiator top right? But as far as timing...i haven't checked that yet.

 

Checking the water pump means pulling it. If there is erosion on the impeller it can cause a situation where you won't get enough coolant flow at higher rpms, but enough flow at lower rpms.

Given what I just said, you need to check the lower radiator hoses too (yes I said hoses- more than one) in order to make sure the inner lining has not started seperating from the casing.

Having it cool down better when the heater is on lends credence to the plugged radiator theory, but you can't automatically rule out some other issues like (I mentioned) ignition timing or water pump and/or hoses based on that. Anything that gets heat out of the system, like using the heater, should make you run cooler.

What is the temp rating on the thermostat?

 

I'm fairly certain its a 190.

Burped it again yesterday...we'll see if that does anything.

 

can't you pick up a new radiator for fairly cheap? Last time I purchased one I think I paid $110 bucks, that was around 5 years ago.