I just bought a '91 XLT Explorer 4x4. The engine has good oil pressure, a clean air filter, doesn't smoke, miss, or knock, but it's slug. Here are the specs: '91 XLT, 4.0L, 5 spd, 4x4, 3.73 gears, 30x9.50x15 tires, and completely stock. If I dump the clutch it won't even spin a tire on the...