High pressure in radiator

truck has been stored for 2 years, i find no water leaks, no oil in the water, and no water in the oil. the pressure in the radiator goes up just after starting the engine long before it can warm-up. my father thinks the water pump is sucking air in and needs changed, i already changed the radiator cap thinking it wasn’t working right but i drove it 60 miles without overheating, what am i missing?

It’s an internal engine problem. Is the engine a 4.2L V-6?

no it’s the 300 cid straight six(4.9l)