For 3,000 miles mine has shown exactly the same. It doesn't matter if I drive highway from fill up or it's stop and go. The end result is close to the same variance.Shutterbug57, I drive a '15 limited with about 42k miles and ever since it was new the computer mpg has consistently been approx 1.4 to 1.6 mpg higher than when I hand calculate it.
I too don't understand why this is, or how they calculate mpg. Must use some kind of "new" math other than how many miles traveled divided by how many gallons it took to drive those miles.
Keeping track of mpg is a good indicator of how well your truck is running or whether something needs attention.