This is mainly addressed to Loren but anyone with anyone is welcome to contribute (keep in mind that this is my 37mpg record holding DD which is rated for 19/24 and got 17mpg when I used to race stoplights)

I finally replaced my bad O2 sensor. Car is running full rich 100% of the time according to my gauge, no surprise there but I had kinda hoped I could get it down simply by plugging the O2 sensor in. I'm now thinking that my thermostat which I've been speculating has been stuck open for as long as I've owned the car is preventing my CTS from reading a temperature high enough to get the car out of warm up enrichment or whatever. I fully intend to replace the thermostat the next time I have to crack open the coolant system for any reason (gas ain't cheap but neither is antifreeze). In the mean time I'm planning on creating a controlled vacuum leak to lean it out at least at idle.

I began to question my transmission gearing a little bit ago, I've always heard that Corvettes and similar cars get their fuel economy from how high their 6th gear is, I've also heard that you don't want to run an engine too slow or (obviously) too fast for FE I know on a Saturn 1.9L I read up on BSFC and decided that I should keep a Saturn between 2000-3000rpm. Using that logic and popular opinion over at the Nissan forums I figured keeping it between 2000-2500rpm was the best thing for it. Now with overdrive on cruising 55-60 miles an hour I'm under 1800rpm so I'm thinking gearing might be too high for best fuel economy? In theory if I rewire my overdrive lockout switch (removed it last year because I've NEVER used it, nor did my parents) I can get torque converter lockup in 3rd gear and my RPMs should be around 30% higher which would put me at around 2400rpms. Do you think I could possibly see any gains from that? Especially seeing as 3rd is the 1:1 ratio and I've always heard that's where the least losses occur in transmissions (or at least some of them)

I've also been planning to get some cams for a while now because even though I love my gas mileage I'm a performance guy at heart. Engine is a SOHC 3L V6 with stock like 250ish duration, I'm looking to move up to a 266 or at the most a ~270. The most expensive option is JWT Billet S2 cams with a 266 duration ($460!!!) these have the biggest @.050 duration of the ones I'm looking at so I REALLY want these since in theory they should make similar power with less overlap than the other guy's 280s (and because of the lower overlap should retain if not improve my bottom end). Now the 270s I can get for $180, they are reground so a little bit more headache with shipping and core charge and all that. You think that I can keep getting the same gas mileage I've been getting with these moderate cams?