DRAC advise

[cuervo]

I'm trying to correct my speed. My speedo says I'm going 74 when I'm only going 70(gamin speed)

My calculations give me .859047618 and the numbers that are close to mine are:

0.845703

0.854980 < this is off by 4 mph at 70, should I go with 845 or 864?

0.864746

I need to slow down the speedo.

 

[cuervo]

0.864746 got me to within 1 mph.

 

[BGKYK5]

I would have thought you could get closer than 1 mph.

 

[cuervo]

It might be. I need to get on the hwy and set the cruse controll to check it for a long period of time. It also magnifies off set the faster I go. So it could be dead on at 45 and off at 75.

 

[dyeager535]

Tire size outside of what GM anticipated probably means you won't be able to get it dead on. 1MPH off at 60 is nothing IMO.

 

[77crewcab]

I am needing to do the same thing after a gear change. How do you adjust it/where is it on a 90?

 

[cuervo]

I am needing to do the same thing after a gear change. How do you adjust it/where is it on a 90?

It should be under the dash on the left of the steering column.

http://www.tbichips.com/drac/

This has all the info on doing it.