I cannot recommend Scan Gauge highly enough. We just returned from a 4,000+ mile trip, I run ours with coolant and transmission fluid temps along with real time and average mpg. I do care about mileage and the Scan Gauge makes it easy to get the most out of the V-10 beast for the least amount of fuel. For the record we averaged 9.5 for the entire trip and highway cruising at 60 was always 10 or better.
Send me a PM if you need the codes for transmission fluid temps as it is an "X" gauge function that needs to be programmed in (very easy to do). :C