GMC Repair: milage/smog check prep, champion truck plugs, smog check

Question
Good Morning, I have an 02 Sierra 1500 SLT 5.3L with 93k on the Odometer. I have a SMOG Check due this year for my registration renewal and my mileage has been down from 17-18 mpg to 12-13 mpg for over a year (it has not been addressed because of unemployment). It has been suggested to change the spark plugs, going with the Champion Truck Plugs. What plugs would you recommend?

I am also aware of a problem with the AC Compressor coming on without any command from the dash controls (it cycles on and off by itself)(from the AC switch or from the selector being in the defrost mode). I changed the control module with no correction to this resulting from the new controller.

Answer
Hi
Before I change plugs, I would change the fuel filter and air filter.
A drop that significant in MPG is severe. I Also if replacing plugs would go with Delco iridium tip.
Does the vehicle seem sluggish? IF so check and make sure a brake or park brake is not stuck. This too will adversly effect mileage.
The issue is also in the programming of the PCM, so the computer should be reprogrammed to help corerect the phantom compressor cycling.
I Hope this helps
Good Luck
God Bless
Pawl