How and where do you generally use the car ? If you are in a downtown, stop and go traffic all of the time, you might want to step up to a warmer plug. But the spark plug recommended by GM is usually pretty much a good one to stick with. But if you were on the highway most of the time, ( And assuming your having carbon build-up ) then you could use something warmer, but what is the trouble with your existing plugs ? why do you want a hotter plug ? Build-up can come from a number of reasons, leaking intake valves could be leaking oil into the combustion chamber, but a number of sources can cause build-up on the plugs, what do they look like ?
First let me welcome you to DC. Now like Zyphra said why are you inquiring about heat range for spark plugs. Are you fouling them? Experiencing Peoformance issues. Why would you want to change the heat range on your plugs. Without information one can’t make a suggestion.