The next step was the speedometer correction. This truck was equipped with an ABS sensor that required separate, in-line compensation to the gauges, so the dash had to be pulled apart. It was a little unsettling to pull at the dash of the truck, but the clips released without much fuss. | 
The panel on top of the gauge cluster pulled up and out, and was held in place with the same clips as the dash trim. A T-15 Torx bit was used on the gauge bezel. |
If you'd read the directions carefully, unlike us, you'd have pulled the bezel off at this point to make it easy to reach the 7mm bolts that hold the gauge cluster to the dash. It's possible with the bezel in place, but it requires a wrench, which is much slower than a socket and ratchet. | 
The Hypertech inline speedometer calibrator needs to be programmed first. It was plugged into a PC with the supplied USB cable. Once we filled in the specs for the factory tires and gears with the new tires and gears, we got the correction factor of .952994, which was then uploaded into the calibrator module. |
The calibration module plugged into the back of the gauge cluster. | 
There was just enough room behind the gauges to stash the calibrator module out of the way. We reinstalled the dash and we were done. |
From the Driver Seat
After the new gears were installed, the noise was gone and the truck felt like it did when it was new. The gears corrected the tire height, and the added power from the programmer, plus the extra power we picked up from the intake and exhaust has woken the truck up. Best of all, the mileage improved from a dismal 12 mpg average to 15 mpg, a 25-percent improvement. That's the mileage we were getting from a stock '07 Silverado! The Mag-Hytec differential cover provided added peace of mind; the increased fluid capacity, cooling fins, and magnets will all help the gears last longer, and the dipstick will make it much easier to maintain. The speedometer calibrator finally made the gauge accurate, but with our new gears we were less than 5-percent off anyway. The real benefit is the ability to change tire sizes and update everything in the matter of an hour.
Your Questions Answered
| TIME SPENT WORKING: | 7 hours |
| (6 for both differentials, 5 minutes for the programmer, and 45 minutes for the speedometer calibrator). |
| DEGREE OF DIFFICULTY: | Advanced |
(Due to the specialized parts and importance of proper setup, gear installation is difficult. However, anyone can
install the differential cover and programmer.) |
Tools Used:
Sockets, an impact wrench, bearing puller, press, dial indicator, and micrometer
| PARTS USED: |
| Hypertech Max Power Programmer | PN 32004 $379.99 |
| Hypertech Speedometer Calibrator | PN 730102 $209.39 |
| Mag-Hytec GM 10-bolt 8.5-inch cover | $250 |
| Sierra Gear and Axle 8.5-inch GM 4.56 | $125.40 |
| Sierra Gear and Axle 8.5-inch GM '99-up master bearing kit | $78.97 |
| Sierra Gear and Axle 8.25-inch GM IFS 4.56 | $148.50 |
| Sierra Gear and Axle IFS install kit | $69.63 |
| TOTAL: | $1,261.88 |
| (Not including tax and labor) | |