Engine/Transmission (1998.5 - 2002) Trip Computer accuracy?

[VIPERBLUELX]

When I first got my 2000 the trip computer would show around 16mpg average. This was with stock tires. I put 315/75/16's on it and then had the ECM reflashed for the new tire size and it still showed around 16mpg. Now that I've installed the BHAF, muffler delete, and TST Powermax it's up to 19mpg. Do those mods usually give that good of fuel economy?

 

[WestTN]

Fueling boxes cause error. The computer thinks it is injecting less fuel so it shows improved economy. I just returned home from the races at Bristol and the mix of towing and solo running netted me an actual 14. 5 mpg thanks in part to my Smarty. However, the trip computer said it was 16. 6 mpg. When I run the stock tune my trip computer is accurate within 3% or so.