2003 Pontiac Montana Tempature gauge goes higher than norma

Make sure if engine temp gets anywhere near red mark that thermostat is opening and cooling fans are coming on. Thermostat is in engine side of top radiator hose, hose should get hot to touch when engine reaches 200 degf. Cooling fans are located between engine and radiator and you can hear them running if you open drivers side door while stopped and engine is hot.
To confirm fan operation open hood and feel between engine and radiator while engine is hot, you have two fans, make sure both are operating at same time, they have low and high speeds. DO NOT touch fans while running you could loose a finger, just feel for AIR moving across front of engine FROM FANS.
Head gasket failure is very common on these vans so make sure it is not getting over 230 degf. Or you will be forking out cash for new heads or new motor.
I would say something is not operating right and have it checked out ASAP.

As pointed out in the first post, you may have a thermostat going bad (lets water through too quickly, and doesn't provide proper cooling).
The other thing you need to check is to see if you have a coolant leak. Head gasket and intake gasket leaks are very common on these engines. A shop can do a coolant system pressure check (and should before replacing a thermostat) to let you know if you have a problem of leaks.