I just bought a 4" lifted 06 X with 33" tires. its been at the shop since the prior owner ran all of the oil out of the rear differential and wacked the control arm so i've had new 4.10 gears put in, new lower control arms, new bushings and track bar. jsut got it back and feels like the speedo is off alot. i thought with bigger tires the speedo would read slower than actual speed but with a GPS i'm atcually going 10 miles per hour slower than the speedo says?? not sure if the prior owner put in a new speedo gear for 3.07 gears and 33" tires but, if he did would that be why i am going slower than the speedo says??