Billy, I would ask your dealer about the i/r sensor but from a dealer it'll be expensive (still less than loosing your car) but if they say it'll work and is included get that in writing.
Good advice. Was looking through my owners manual and the factory alarm does detect change in vehicle inclination. Sorry.. I read your post wrong. Thought you said didn't have. My bad!
But.... like you said, having all that installed by the dealership would be very expensive!