2006 Yukon Denali suspension question

[Black GT]

I have a 2006 Yukon Denali that recently had the "service ride control " light came on.
I've been doing some searching on the internet trying to do some trouble shooting but come up with all kinds of different symptoms, I recently checked all the fuses (all checked out good)
another thing I see is it may be a sensor or the compressor for the air ride.

Where would be a good place to order these parts from, first off I will probably bring the truck to our local chevy dealer and have them diagnose it to find out for sure what is wrong, but from what I've been reading the parts from the dealer are way overpriced.


Thanks for the help.