how do i find out which exact part i need. i.e. where do i find the exact info on the car
It's fairly simple.
Take your VIN number and when looking for a part on one of these car parts website there will be a place to enter your VIN and all the info will come up and for future reference you'll know if it's a 2500 or 3500 or 1500 model.
And once you find the mirror you need take the part number and Google search it.
That will get you the best price.
Sometimes it might be worth swapping out the whole mirror.
Assuming you did no damage to the casing many times you can replace the mirror part itself.
When entering the VIN it will show you the exact mirror, whether it was heater or has a side blinker and or folds and ....
Good luck. And if you need more help, willing to help you.