I agree with everyone here - the 4.3 is a bit of a pig because it just doesnt have the power to move a vehicle that heavy. Even in 2011, it still only has 195 horsepower and 260 ft.lbs of torque. I also agree that its possible that a change in the gas where you fuel up could cause your recent MPG drop. Also, like enkei said, you might be able to get 1-2 back just by adjusting your programmer a bit, depending on how it is set now.
One more suggestion I have is to clean your Mass Airflow sensor, especially since you have a K&N intake. Over time, the mass airflow sensor can get dirty and cause poor performance and fuel economy. The oil on K&N filters also has a tendency to coat the mass airflow sensor and cause problems with it - particularly if you might have over-oiled it at some point. To clean the sensor, you just need to pick up some mass airflow cleaner (safest to get this because other cleaners could damage the sensor) and give it a good spray. let it dry and then reinstall it.
One more suggestion I have is to clean your Mass Airflow sensor, especially since you have a K&N intake. Over time, the mass airflow sensor can get dirty and cause poor performance and fuel economy. The oil on K&N filters also has a tendency to coat the mass airflow sensor and cause problems with it - particularly if you might have over-oiled it at some point. To clean the sensor, you just need to pick up some mass airflow cleaner (safest to get this because other cleaners could damage the sensor) and give it a good spray. let it dry and then reinstall it.
