Mpg drop

Over the last two tanks of gas I've run through, my mpg has been about 16.5 for both of them when before I was constantly getting 19.5 to 20.5 mph. I feel like that is a significant drop and I haven't done anything out of the ordinary. I last checked my mpg a few months ago when I was running different octane gas through it to see what I got.
I don't drive insanely fast (reckless driving ticket slowed me down but even when I did my mpg was higher) I drive on mostly flat land and use cruise control when I can. I usually stick to highway driving so very little stop and go city traffic. I don't tow or use 4x4 often (mainly driving to and from work and driving around in rural areas). No lift kit or aftermarket bumpers or anything, just a stock truck
I've done all regular maintenance, tire rotation, oil changes, spark plugs, recent transmission flush, greasing drive shafts, differential, air filters, and t-case oils. I don't put any additives in any oils or gas I use. The only thing I have is an oil catch can but I've had that since last September and hasn't affected mpg that I saw after putting it in.

Just wondering if there's any common issue with these trucks that would cause that or if there's something certain I should look into. I'll keep an eye on my mpg to see if anything changes

 

Is the cel on?

 

Nope no cel or any lights flashing

 

Checked tire pressure during the last 2 tanks?

 

Checked it yesterday 3 were at 30 and one was at 32, I keep them at 30 based on the door sticker

I let the one down to 30

 

Just throwing this out there, don't know if it has anything to do with what you're seeing, but 70 mph on the highway seems to be the tipping point for these trucks. Go over that, and the mileage takes a nose dive.

 

Speeding. Pay attention to the road, not your phone.

It's the American way. Go 85 mph. Complain about gas mileage.

Who's noticed the massive about front end bumper humper collisions? 90% of wrecked cars I see, have smashed front ends, lolz. Auto body shops are making a killing.

 

Well damn most of my drive to work the speed limit is 70 so if course I'm going a few miles over that I just didn't think it would impact the mpg that much though but if that's what it is I guess I'll just have to deal with it

 

70 is the breaking point for mine also 65 avg 18, 70+ right at 15.5-16.

 

Drive no faster than 70 and put a little more air in the tires. With P series tires on my Tacoma I ran about 35 PSI. Last set I bought are E rated LT series and I keep them at about 40 PSI.

Driving into a headwind will hurt you to. I did a cross country road trip 2 years ago and averaged right at 20 mpg over about 5000 miles. Some tanks were in the 22-23 mpg range. Some in the upper teens. But on the way home I hit a steady headwind from Denver to Kansas City. I still kept the same speed, ~ 70mph, but my fuel mileage on that stretch was in the 16's.

 

Consistent highway driving under 70 mph gets me 21+ mpg. I do a lot of 60mph-65mph. Go over 70 and it drops as stated above.

 

Not saying this is your problem... my wife's car started getting bad gas mileage.
I found the vacuum hose for the brake booster was loose. The hose would easily slide off even with the clamp on. I replaced the clamp and the gas mileage was back up.

 

Keep the rpm under 2k. Are you lifted? If so, how much?

 

Lift wheels and check for brake drag
bad alignment can affect MPG
MAF sensor can do weird things when dirty

 

Also could be a 02 sensor on its way out just a thought.

 

If I go above 65 I’m already assuming I’ll have lower mpgs. I got 18.5-ish on an all freeway trip recently!!! Lol

 

Check your brakes. I had a caliper stuck, couldn't tell until it wore out the pad on my car. Mileage jumped back up once i did the brakes and fixed the issue. Saw a 3 mpg decrease. I just thought it was the colder weather.

 

I agree 100% with the over 70mph mileage tipping point, but since the op's problem happened so quickly I'm inclined to believe that something mechanical went wrong.

 

Thanks for all the suggestions everyone I'll look into them and see what I find. How can I tell if a caliper is stuck? I just rotated my tires 2days ago and when I checked the brakes on both sides the pads were pressed against the rotors on both sides. Drum brakes looked fine, I cracked the drum open and cleaned it out nothing looked abnormal back there