Computer Upgrade and MPG Change

I have read on some post about suspicion of MPG reduction after a Computer Upgrade. Not my intention to start a new topic on that, but I did not find that post.

So, thought I would start a post with that topic as Subject.

My Example on a car with 21,000 plus miles that had average (per Fuelly) of 51 MPG (maybe slightly less on a few HWY trips). I had a recall done (relay contact replaced or something) and they did a Computer Upgrade on 12-19-2018.

Then we did the following trip after a fill up on 01-03-2018 at 20,7000 miles that computed to 49MPG (some drop there from average of 51MPG).

THE TRIP:

01-04-19 at 21,112 miles for 422 miles traveled to Leland, NC area used 9.74 gallon at $2.199 at EXXON. That comes out 43.3MPG. A HWY trip at mostly 55 to 70 MPH, but that is say 4 MPG or more below any other HWY trips. NOTE: I had a recall done on 12-19-2018 and that included a computer update (???? - maybe cause of MPG drop).

01-13-19 at 21,345 miles for 223 miles travel in the Leland / Wilmington, NC area used 4.81 gallon at $1.959 at Circle K. That comes out 46.4MPG. I would say 50% city at 35 to 45 MPH and 50% HWY at 45 to 55MPH.

NOTE: A bit better than the 43.3MPG HWY trip, but still about 4 MPG below our average. NOTE: Again, I had the computer update on 12-19-2018.

01-14-19 at 21,770 miles for 425 miles traveled back to Sevierville, TN area used 9.176 miles at $1.929 at Weigel's. That comes out 46.3MPG. A HWY trip at mostly 55 to 70 MPG. That is better than the trip to Leland (43.3MPG going, 46.3 coming back, and about the same as MPG on local driving while there).

NOTE: I say again things seem to be 3 or 4 MPG less than my average of 51 MPG for 20,000 some miles and had the computer upgrade on 12-19-2018.

It is a EX Model with the option that includes the Sunroof purchased in Feb 2017.