LMM Fuel Economy

[mgscustomtune]

Here is a few pros and cons in the way mileage is calculated
When you calculate by hand you have no control over the temp factors,wind,grade to a given point which all effect the rolling stance of the truck. l recently did a calculation using a GPS and the on Board readings. I went 25miles constant speed 55mph pulling a 10,000lbs load the GPS and on Board Computer matched up exactly in distance with an average of 12.5mpg on the Computer. The next day which included some tempature change (5degrees higher) and wind(almost at zero) did the same trip. I got 13.5mpg. The on board PCM calculates the mpg including the wind/grade of road you are traviling on and temp change where calculated by hand you do not include those factors. I also took out a 2008 5.3 l was tuning at my shop drafted a transport on the HWY at 55mph l was amazed watching the onboard compter change from 22mpg not drafting to 25mpg when l drafted the the transport l think the onboard computer are a little moe acurate than we think. It is no secret that the New Exhaust Filter System hiders gas miliage and the amount you can strech the Custom Tune without a Delet of the System. Just my two pennys worth