The smell is normal on GMC vehicles. You may have carbon build up. I can think of ways to fix this. 1) blow the carbon out by going on a hard heavy footed drive for about 2 hours , pedal to the metal only. 2) Take your pcv valve off the intake hose and get a glass of water , with the motor running put the pcv valve into the glass of water , be very fast when doing this so you dont suck to much at a time. 3) Buy a throttle body cleaner thats safe for your throttle body. Ask your dealer what is safe to use. Follow instructions on the can , should work fine. 4) Moto vac cleaning , take to a dealer that can do a moto vac , it cleans all you intake ports and should cost around $80. Any of these should work fine , try in the order i gave you so you can save money. Also , once youve blown the carbon out , your car will have more power and response like when it was brand new. Message me and tell me your progress.