Going with a set of 4.10 gears will help out a lot. City mpgs will get probably 2-3 better because your main enemy is the ECSB 4.8 with 22" rims. With 4.10s, your motor and drivetrain won't have to work as hard to get the pig rolling. Hwy mpgs will either stay the same or get slightly (1 mpg) worse. I would recommend going to 4.10s. If 4.10s seem a bit to high for your needs, you could always get a set of 3.90 Yukon gears...