soooo... i think i'm doing something wrong

[dongs]

I'm reasonably new to ecomodding/hypermiling and a week and a half ago I took the first step towards improving my FE by installing a vacuum gauge. I'm pretty limited income wise so a scangauge is out of the question for the time being.
About 90% of my driving is commuting to and from work, the entirety of that is on a 2 lane 35 mph road/hwy through a couple stoplight infested towns and rolling hills. I've got a 2002 S10 with the 2.2 motor and a 5 speed and I had been averaging 22-23mpg or so before installing my vacuum gauge, with my last tank at 22.8. I also rotated my tires and while I was at it upped the pressure a bit (they were a bit low now they're at 40 psi, manufacturer recommends 35, sidewall is 45).
Well, I filled my tank today for the first time since adding the gauge and my tank mpg was 23.58, an increase of .78mpg or about 3.5%. I guess I was expecting a slightly larger increase, especially since my driving habits on my route have since changed quite a bit. I realize calculating tank to tank mpg by dividing mileage by fuel added isn't the most accurate, and in Oregon you aren't allowed to pump your own gas(in fact when I filled up today and did my calculation I figured 27.2 mpg and about sh!t my pants until I started my engine and realized the goober pumping my gas was about 1/8tank short of full. Then I don't know if he 'topped it off' when i asked for him to pump it again since it wasn't full)
Anyhow, is 3.5% a reasonable increase?
I've been thinking for a while about replacing my upstream o2 sensor since my truck is 11 years old with 131,000 mi. Do you all think that would be a reasonable investment?
It's about time to change my oil and I'm thinking while I'm at it I'll swap the trans & diff fluid to synth. I've run mobil1 in my motor before but it sure was quick to point out a leak in my rear main. I've been running conventional HM since then with no leaks to speak of but I may switch to mobil1 HM to see if that helps at all

[brucepick]

Synthetic will find leaks if there are some. Your call on whether you want to try it again. Synth will usually give you a tiny FE assist, I think mostly before fully warmed up when synth stays thin like it's supposed to.

The steps you took are good. If you go to same pump all the time that might help with consistency. Keep at this game and you'll see more progress. It doesn't come all at once

Upped tire pressure always helps. Don't be afraid to go to sidewall max, when tire is cold in am. Pump it up past your target when convenient during the day. Then check before leaving in am and bleed off some if needed.

For bigger gains I recommend some coasting. At first with engine idling. As traffic allows, accelerate to maybe 5 mph over your basic cruise speed. Put in neutral and coast. At 5 mph under the speed, go back in gear again and accelerate up again. Hopefully your cruise speed allows 5th gear. It's possible a truck will coast so badly, you will lose speed to fast to do much coasting. You just have to try it. I coast with engine off, but it takes some time to get the hang of that.

Another big area to work on is aero. Look at some truck threads in the Aerodynamics subforum. Pickup truck aero drag is usually pretty bad so I'm sure it hurts you even at 30 mph. Read some aero threads. Easiest fastest thing is a 2' to 4' plywood sheet across the back of the bed, by tailgate. Like a substitute tonneau cover. Cover it all if you can, but if you only cover the back portion it will help. Ford tested it and recommend it. Keep the tailgate up.

The good news is, it's pretty easy to work on the bed and on the underside too. You'll also find aero threads on front air dams. Lots of pickup truck modders use one, and pretty easy to make.

Good luck!

[Gealii]

+1 Bruce and about the O2 sensor if its not throwing a code i wouldn't bother changing it out. The PreCat sensor will affect your mpg's but they are sensitive and if not throwing a code it should be fine.
And just remember your gains might be small now, but as you continue to drive the same route while hypermiling the more gains you will see over time.

[dongs]

Thanks for the assurance. I'm 7.1% over epa, 17% when factoring in all the city miles. It's a challenging route to work. Lots of hills and a looong steep grade after a stop for my drive home. I've been able to 'pulse' up the small hills and glide for 1/4 mile or so. The plus side is I work at 6am and leave around 530 so I'm the only car on the road, the down side is it's pretty chilly out at that time and the drive home I'm surrounded by soccer moms in their minivan rocket ships.
I've got a canopy on the bed right now but it's far from aero, it came off an old chevy luv and doesn't even come close to matching up with the back of the cab. I may ditch it come summer and build an aeroshell and belly pan if I'm feeling dedicated.
For the time being I'm trying to maximize mpg with a stock truck.

[dongs]

*on the plus side, having installed the vacuum gauge I did a thorough check on my engine health and everything looks to be in tip top shape! Not bad for a GM motor lol