ISUZU OTHER INSTRUMENT CLUSTER GAUGES SPEEDOMETER

I Have A 1995.5 Isuzu Rodeo Witho Only 66k Miles With A V-6 Engine. My Gas Milegage Is Horrible. I Recently Had All The Belts Replaced...

I Have A 94 Isuzu Xls V6, The Speedometer Went Down To Zero, Then Later On It Went Back Up. Why Is This Happening? Can A Speedometer Be...