This information is in addition to the "Tires" portion located in Section 5 of your owner manual.

When tires are changed from the original equipment size to those adapted to railroad track gage, the Vehicle Control Module (VCM) must be reprogrammed to correct the speedometer reading.

Truck Models C/K 2500: LQ4 6.0 L V8 Engine and MT1 4L80-E Automatic Transmission. The transmission calibration part numbers are as follows:

GT4 Axle	12578772
GT5 Axle	12578773

Reprogramming the VCM is done with a TECH II electronic diagnostic system. Your GM truck dealer has this equipment. Your dealer has the correct calibration identified by the calibration part numbers on the following chart and any later updates after this publication.

New Tire Size	Axle Code	Calibration Part Number
8-19.5 Custom Xtra/Super High Miler 593 Rev per Mile (368 Rev per Kilometer)	GT4 (3.73:1) GT5 (4.10:1)	12583798 12583799
8R19.5 Vandura Commercial/School Motor Home Chassis 608 Rev per Mile (378 Rev per Kilometer)	GT4 GT5	12583800 12583801
G133 Unisteel 8R19.5 626 Rev per Mile (389 Rev per Kilometer)	GT4 GT5	12583802 12583803
Please refer to the light duty series GM BODY BUILDER BOOK for further general information regarding vehicle modification.

This information is in addition to the "Tires" portion located in Section 5 of your owner's manual.

When tires are changed from the original equipment size to those adapted to Military Vehicle usage, the Vehicle Control Module (VCM) must be reprogrammed to correct the speedometer reading.

This reprogramming will also limit maximum vehicle speed to 93 mph (150 km/h).

Truck Models K 2500: LLY/LB7 6.6 L V8 Diesel Engine and M74 Automatic Transmission.

Reprogramming the VCM is done with a TECH II electronic diagnostic system. Your GM truck dealer has this equipment. Your dealer has the correct calibration identified by the calibration part numbers on the following chart and any later updates after this publication.

Model Year	Engine	Transmission	New Tire Size	*Calibration P/N
2003/2004	LB7	M74	LT285/75R16 (628 Rev/Mile) (389 Rev per Kilometer)	15130245
2004	LLY	M74	LT285/75R16 (628 Rev/Mile) (389 Rev per Kilometer)	15130246
2005	LLY	M74	LT285/75R16 (628 Rev/Mile) (389 Rev per Kilometer)	15130247
Please refer to the light duty series GM BODY BUILDER BOOK for further general information regarding vehicle modification.

*New calibrations include maximum vehicle speed of 93 mph (150 km/h).