In this case, they didn't charge me for the computer adjustment. I made several trips there claiming it was warranty work from previous tire and wheel change. I went from 20 rims to 18" rims.
When they checked the computer they went by the tires recorded in the VIN record. It threw off mileage and gps calculations. I proved it by using a handheld GPS. It still took them another try at getting it right. A new tech on the Quick Lane found the error. with the ECM input on tire size.
If there wasn't a difference in the overall diameter size, why would there be a menu on their computer showing the different tire sizes between the 275/55 R20 and 275/65/R18?

 

Saratoga.

 

Um, truck tire tread is ~13/32". The 2 tires he listed are 1" diameter difference. If the larger tires lose 100% of the tread, completely bald, they would have lost ~26/32", which is less than 1". That is still larger than the brand new smaller tire.

 

According to GPS I am 1-2mph faster at 75mph according to the analog gauge.

Update: So far I am holding strong at 14mpg. Leaning towards bad fuel.

 

I have to keep mileage logs for work and since 2014, my mileage on my 2012 Ecoboost/3.73 gear has consistently decreased. I think a lot of it has to do with the catalytic converters slowly becoming clogged up, although they still meet the threshold of working properly. I change oil ever 5k miles, air filters every 10-20k, spark plugs every 30k miles, done pretty much the same routine for the last 4 years, no change in driving habits, same exact tires (replaced with new sets of the same thing), etc.
2014- 15.6mpg (60k miles)
2015- 14.47mpg (90k miles)
2016- 13.82mpg (120k miles)
2017- 13.19mpg (135k miles)
2018- 13.12mpg (YTD-147k miles)

Truck runs perfectly fine, however, I've noticed what seems like a slight decrease in power when giving it the ol Italian tuneup. I'm almost positive a new set of converters would restore it back to the 15+ mpg range.

 

Is there a way to clean the cats? I don't mean regenerate the substrate, but just remove the carbon from the exhaust?
What about pouring acetone or some kind of solvent down the pipe backwards? Simple green?

 

Don't believe there is a way to "clean" them to be honest. I've been wanting to try to pick up a set of aftermarket or going off-road with a tune to see if it helps, but I just haven't fooled with it, as it is getting near the time for me to replace the truck with a new one.

 

I'm pretty skeptical it has much if anything to do with cat performance. My truck has been catless for around 40k miles and my mileage is pretty close to the range y'all seem to be thinking is "less than" you've seen your truck perform in the past. My truck averages about 11-13 city and the most I ever saw hwy was 19mg with OEM spec tires -- and that was one time. Usually hwy I'm 16-17mpg with cruise control @ 75mph.

PSI, for those mileage quotes you listed I feel it's impossible to really factor in the type of driving associated with the fuel economy numbers you listed.

There is something to be said about overall engine performance going down over time but I think the 13mpg you listed isn't the mileage you're getting on a 300mi hwy trip with cruise set @ 65mph...

 

Well I think I'm going to say I have been buying bad fuel. Ever since I have filled up with the Costco fuel I have not seen a loss in mpg's. Holding strong at 14mpg this morning and drove a bit more aggressive at that. At this point the last couple tanks of fuel I would have already been at 13-12.5 mpg. This is with normal commute on the feeder and sometimes on the highway, stopping and idling for short periods of time while I walk my houses, etc. Looks like I will not be buying gas from QT anymore. Costco is $0.20 cheaper anyway. If anything changes I will update.

BTW, as far as the Ecoboost's go. I haven't heard anything good about long term fuel mileage. I hear they drop off the deep end fairly quick. One of the reasons why I stuck with the tried and true 5.0L. Second biggest reason is it sounds better.

 

It's most definitely not HWY mileage. It's the same 70 mile round trip (consider it city mileage really, even though its country back roads most of the time) to work and back for the past 4 years. Cat performance was my only thing to fall to, as my truck runs perfect, and my last two blackstone labs report indicted my engine is wearing at the pace of an engine with half my miles, and all categories are well below average. It's not using oil, has a clean air filter (clean sensor at every air filter change~10-15k), spark plugs every 30k. It's either that or carbon build-up, even though I have no symptoms of indication of severe carbon buildup (rough idle, stumbling, etc). Might be a small combo of both, never know.