2004 Sierra 1500 speedometer calibration

[virginiasquire]

I have a 2004 Sierra 1500 2 wheel drive with 4.8 engine. My problem; I have changed the rear end from the 3.42 to a 3.73 positraction for trailer towing. The speedometer is now off by about 7 mph at 65 (actually 58 by gps). I understand that there is no dealer calibration by flashing the computer. What is the best and/or most efficient manner to recalibrate the speedometer? Thanks.

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[92chevysilvy]

You could put on tires that are 4 sizes bigger... That is about an 8mph change.

I'm just kidding. I'm sure one of the guys here will know an answer. but welcome to the forum!

[RUFFNECK4LYFE]

You gotta get a tuner. Either a handheld like Superchips or Hypertech, or a custom tune. The handhelds cost bout $350. The custom tunes are about the same or less. Unless you are also looking to upgrade the performance, the cheapest way is to just keep using ur GPS.

[virginiasquire]

I have been looking at the Hypertech inline but don't understand the price difference between the inline and the other Hypertech model. One is around $300 web price and the other is around 190. I think I saw both at either Summit or Jegs.

From a performance standpoint, economy will be my focal point. I'll be towing a 7000# trailer when I retire very soon (66 next month). Will the tuner help improve gas mileage? Thanks

[RUFFNECK4LYFE]

Oh of course my friend. Getting a handheld has been more popular for trucks that pull some weight. Cause of lot of them change the rear end ratio or add bigger wheels and tires. Performance wise it will give you more torque and better gas mileage. I had a Hypertech and paid 350 for it. It was ok but I wanted something more specific. But I am sure you will be happy with a handheld. Hypertech is ok but there are others that may work better. Like Superchips, Bullydog, etc.

[bharmon444]

There may not be that big of a difference with your speed, the GPS registers about 3 to 4 miles per hours slower then real speed. I know a police officer and we used his radar gun , to determine that its the GPS thats slower

[RUFFNECK4LYFE]

Thx for the info! I was always wondering that.