Engine/Transmission (1998.5 - 2002) Power up mileage down

[tractorface]

My mileage has been down from 19 to around 16 for the last 6 month's but I swear the truck feels like a Hot Rod. It really seems to be running well. I really don't drive any different than I used to. Always running hard unloaded. Any ideas? No tire change or anything either, same diesel station, etc. etc.

 

[CFAR]

Have you checked your IAT, try cleaning it, some have gotten their mileage back by doing so. I know some of them had exhaust brakes which caused soot build up. Its worth a try.