What will cause a 'p0506' code?

not exactly sure but a similar prob on my pathfinder points to the TPS (throttle position sensor) but it may go by a different name for your make. also since its a GMC product you might have a metering sensor to change. i think this is call a MAP or MAF sensor, very easy to DIY but the sensors are anywhere from 80 to 200 bucks. as for the actual code identification, what i have found is that auto zone in my area, will read the code, tell you what it means and sell you the part if you wish to buy it. no high pressure and they dont charge for the diagnostic read and id.

answers on blogs like these can take you down many paths. i'd say that since you have the code number your best bet is to go to a mechanic shop or parts store and let them tell you exactly what that code means. parts stores are usually very good at id-ing things like that and they have diagrams to show you where the part is located. again, you'll get many different answers on these sites and some will be right on the money, but many including mine may not be. use the code number knowledge you have to actually get an accurate answer.

Along with the other suggestions, check/clean/replace the air filter.

p0506 means idle speed low i would clean throttle plate and bore and check for stuff staying on that would cause a extra load on the engine

Also check your pulleys. A bound up idler pulley may not cause a belt squeak and will put a huge load on your engine.

One possible cause is if your fuel pump is not functioning correctly or defective. Also check your fuel pressure regulator.Incorrect fuel supply to the engine will cause low idle that tends your engine to stop.