Just bought an LE, 5-speed, '04 Corolla. With a long highway commute, would an oil change interval of 5,000 miles be acceptable, or should I stick to 3,000 miles? Also, what kind of gas mileage should I expect?

I would stick with 3k oil change intervals- 5k interval is used as a marketing tool to sell the car. It is actually used for most of the newer cars sold today.

As for mileage, I am currently getting 37 miles per gallon on 87 gas-