If you are taking the mileage from the DIC it is probably incorrect due to the programmer. Only results to believe are hand calculated. If it's still off with hand calculation it could be the tune. Without a tune you should not have to worry about EGT's too much as your computer will defuel to keep temps down. Adding the tuner defeats that program. Best way to tune a d-max is by having your ecm reprogramed with EFI. Several guys are really good at it and can tune it to your specific needs. Check the diesel forums or look for Killerbee on this forum.