worst mpg I've ever heard of

As stated earlier, you are running in open loop. It's pretty close to the same as running with the choke on. You are burning more fuel than you need.

Also, check you r thermostat. Is the engine temp getting close to 195 when completely warm?

 

Gutting the cats didn't get you anything but a check engine light....

 

Put functional cats back in and replace O2 sensor.

 

Your answers are here. You have messed up your fuel readings to the computer, it doesn't known what to do. It thinks it's pulling a trailer also.

 

My truck is completely stock, 2015 6 cyl DC...I get 19-20 MPG mostly highway miles driving 70-75 mph. Around town about 15 MPG give or take

 

Same here, stock highway tread Bridgestones, on my commute, which is half 80 mph highway and half city streets I do around 15-16 mpg, highway trips at 75ish mph gets almost 20 mpg, throw in some heavier more aggressive tires, heavy bumpers, it ain't running right with no cats, if they are original 02 sensors they are probably not at their best, plus larger diameter tires that could be throwing your calculations off....problem is you can throw a bunch of money into new cats and 02 sensors, get it running right, and still probably be getting 15 mpg at best for mixed driving. Especially if, like me, you don't drive with much regard for fuel mileage. It should run better, maybe.

 

I get 15 towing a loaded trailer around town, in addition to my armor, tools, and 33s. You guys are doing something wrong, me thinks.

 

I never put any stock in a tonneau cover helping MPGs but I recently got one and have put a couple thousand highway miles on since (drove from MA to NC and back) I used to get 18-19 MPG on the highway averaging about 70-75 mph, got over 20 MPGs on a couple thanks this past trip with the bed fully loaded with family vacation supplies. I have 265/70 17s with no major lift, just 5100s up front.

 

I have an 07 automatic and my tach is almost dead on 2K at 70mph. (v6 auto). Mine's been hanging in at around 20 or so for a LONG time. Your RPM certainly sounds wrong for 60 assuming you are in the highest gear when you measure that.

 

He's a manual.

 

I don't think your friends are liars per se. Well, not about MPG. Other stuff, probably.

But I suspect they have no clue how to do arithmetic. Or average several tanks together to get an even better picture.

Not to make you feel bad, but even my '64 GTO with a 389ci (6.4L) motor and 3- 2bbl carbs (tri power) did that good in town, better on the road. No cruise, no computer.

 

I saw that. But is the manual geared that much differently to drop MPH by 10 for equivalent RPM? I'd expect a 6 speed to perhaps be geared a bit taller since 5 and 6 are supposedly BOTH overdrive ratios.

 

2015 v6b with 26k miles.....mileage has gone UP....21-22mpg combo of town and highway. Keep my foot out of it and it hepls

 

Manuals are higher RPM in final drive gear by a good amount, that's why their mileage is so much worse than their auto counterparts.

 

You are right. It is the NEW 6 speed that has 2 overdrive gears. You can take auto rpm at any speed and multiply by 1.18. They both have the same rear end ratio, but auto is .72 in 5th while manual is .85 in 6th.