Manual Transmission

Unfortunately, yes - this is normal. The manual transmission is geared such that it provides tremendous torque at the low-end but with higher RPMs as a result at the high-end. Manual transmissions lack the "overdrive" feature of the automatic transmission, and a sixth gear. They're made for power, not speed essentially.

If running larger tires than stock, your gearing and (hence) engine RPMs will be affected (which in turn causes the speedometer to be altered slightly as well). One solution is a different ring and pinion set in the rear differential.

The manual transmission in the Xterra has five forward gears and one reverse.