Did you ever adjust your speedo after installing the 4.10's. 4.10's should have the effect of having smaller tires. you wouldn't get better milage speed for speed. If you didn't adjust the Speedo than your putting exta miles on your car that your not driving in addition to not knowing how fast you are really going. by the way the optimum range thing sounds like total bs

when your traveling at 30mph(60mph, 100mph.. what ever) and your rpm's are higher than when you had stock ratio, you are burning more fuel. Emissions is seperate from milage, it just means your burning cleaner.