how can i tell what brand tire pressure monitors i have in my truck

Most likely you have the factory monitors in the vehicle.

The replacement valvle stems i've found are either schrader or dorman

So what? You order them to fit the vehicle application. Why do you care who manufactured it?

each brand is a different style.. not universal

You order them per the application, like a ball joint, tire, or spark plug. Those aren't universal either but all manufacturers make them to fit the intended application. Chrysler buys 80 percent of their parts from outside suppliers and that can change depending on who supplies them with the best price and quality. The supplier could be different even when you buy a replacement from the dealer's parts department.

Be aware there are repair kits available too. I never tried to use one and I don't know if that is a viable solution to your problem, but you might check them out on rockauto.com.