Interesting you say a prius in the winter only gets 35mpg, any direct experience with that or just a joke? My corolla got around 38-40mpg in the winter, summer it was around 40-44mpg depending how efficient I was for the tank. Single trips I could get over 45mpg but never seen it as a tank average. I re calibrated the scan gauge every fill up.
My underbelly plan is to fix rust holes first, undercoat the body/frame etc, then work out an underbelly pan that's easily removable, and isn't too weak to be used off road. In front of the axle will probably be effectively a skid plate, center I'm thinking sheet metal with a frame so it can be removed with 4-6 bolts, and the rear section behind the rear axle doesn't matter much and should effectively never be needed to be removed, so probably sheet metal with a light frame. The rear bumper is OEM and a nice parachute too. It catches slush like crazy in winter lol.
Normally when I replace tires, I go oversized for the higher gearing effect, but for this truck, it seems to be about the perfect gearing for my needs and a mix of mpg. Of course I run max psi side wall pressure (or a little higher). I think the current tires were load range D so 65psi max. I don't really do city driving hardly at all, so the extra spinning mass is offset by the lower rolling resistance and the effect compounds when loaded (less tire sag).
So are you converting you truck to be hybrid, what's your plans on that?
Also ouch on your fuel costs, gas here is about $2.30/gal for 87 octane. Prem 93 (or higher) is $2.72, so mid grade should be about the middle at $2.51. Fuely doesn't have reported mid grade numbers (89 octane).
My LS400 calls for 90+ octane, but it pulls the ignition timing and runs on 87 just fine. The MPG does go down, but the difference in fuel cost, it's cheaper to burn more fuel at the cheaper price.
I wonder if you could somehow smooth out the cylinder deactivation system so it works well with 87 octane. If it worked right, then you might see better cost per mile with the cheaper fuel.
The launch control thing is kind of weird, you have gears, a CVT is variable gearing, it's effectively 1000's of gears, it's not an apples to apples comparison. Personally not a fan of CVT's, but there's pros and cons about them. In a race setup, CVT's can do really well, but for daily driving, I'd rather have real gears.
Anyway, didn't know how the cylinder deactivation system worked exactly, I guess the valves/cam system must use the oil to get the deactivated valves so the O2 sensor will be happy. I suspect the system probably works pretty good when it works, but like you said, when it fails it's not good. Powerstrokes are kind of in the same boat, when there's an injector problem, they are expensive to replace, but the whole engine doesn't need replaced or anything quite that extreme.
I did the math on an overdrive unit for my truck, assuming it got perfect results and the gearing increase gave that much in fuel savings, it would take something like 100k miles to recover from the initial cost of the unit. The propane route for me looks much more attractive since roughly 30% savings at $815 is something like 28k miles. A DIY system that's less optimized would be probably 1/4 the cost. Biggest thing is finding a proper tank for it. I suspect the ones on motor homes mounted to their frame would be acceptable but I'd have to research it a bit more. 20% propane vs 80% diesel would translate to about a 7-8gal propane tank, or ~30lb of propane capacity if I wanted to fill up diesel + propane at the same time.
Also interesting concept, I wonder if a gas engine would see any benefit from having propane added to it. I suspect gas burns more completely, so if there's any gains, I'm guessing there isn't much there. Maybe the octane benefit of propane could be of value though. Of course the computer controlled engines won't like it since the O2 sensor wouldn't be accurate (more fuel dumped in than it knows about).
Based on this page I guess the 6.0L is already a hybrid model? I don't really follow newer vehicles much. Pretty interesting the mpg range though, looks to be typically 17-24mpg.
If I jump over to my truck's year and engine, it's not looking so good, but I'm always at the upper end of the scale vs the average person. Typical looks to be around 15mpg, high end 20mpg.
https://www.fuelly.com/car/chevrolet...=&submodel_id=
https://www.fuelly.com/car/ford/f-25...=&submodel_id=
I wish there was a further break down for gear ratios and such. I don't know how common the 3.55 gearing was for my truck. In the city with normal drivers, I can see 15mpg being the norm with my truck though. With my style of driving, I'm too laid back and slow to get that bad of mpg even when I'm in a rush lol.
My Lexus on the other hand, it's behind on maintenance, same story bought it needing a ton of work. I have to replace the O2 sensors in it from a power steering line valve that went bad (the vacuum idle kick up valve), it ate power steering and killed the sensors. Seeing around 18mpg winter, and roughly 20mpg summer. I do have oversized tires and those are numbers before correcting for the tire size difference (about 5% bigger if I remember right). Looks like I'm getting about the typical mpg out of the car. I wonder if that's because people buying this brand have a different mind set, or my car is just running that bad to consume so much more fuel. It's extremely smooth running, just maybe it's dumping way too much gas.
https://www.fuelly.com/car/lexus/ls400/1990