Hello, I am new to the forum and am looking for some information on my truck. I have a 98 Ext. Cab 4X4 with the 3.4 V-6. When I bought it use it had the TRD bigger Alloy rims on it, but small tires. If I go to 31's like the TRD had will I need to change anything to keep the speedometer/odometer accurate? Also what kind of hit should I look at for gas mileage? Thanks for any help.