I perform regular maintenance,have replaced the motor at 77,000 miles 130,000 replaced the transmission as well.There are no indicator lights on the dash detecting any problems.
My gas mileage has drastically decreased by approximately 200 miles per tank? on 2001 Dodge Ram 1500
Your truck has On Board Diagnostics (OBD2) it would be interesting on a professional grade scan tool to see what the computer in you truck reads as fuel trim values long term on both banks, and looking at Oxygen sensor readings and air flow readings into the engine from the air flow meter or MAP sensor. Does the engine run smooth? Start with the basics air filter, spark plugs and look for vacuum leaks. Its hard to guess without being able to do basic tests first.