97 k1500 5.13 swap and speedometer is all over the place!!!!

[Michaelknight]

So I just dropped a new 383 in my 97 k1500 with 37s and installed 5.13s. Now my speedometer is all over the place!!!! How can I fix this..... please help.

 

[FlyingV92]

Have gone through the checklist of the basics I.e. grounds and speed sensor switch?

Did you do the swap or a shop?

 

[Michaelknight]

Yes sir just changed both switches and all engine bay grounds were hooked back up

 

[stutaeng]

Did you get your ECU reflashed for the new gears?

 

[Michaelknight]

No I gave not

 

[Michaelknight]

Have

 

[kennythewelder]

The speedometer is calibrated by GM for the OE tires and gear ratio. Once you change ether or both of those, the ECM must be recalibrated for different size tires, and a different gear ratio in the differential. All if this works off of the Vehicle speed sensors, and so does the shifting of the transmission. If the speedo is acting crazy, then the VSS may very well be going out

 

[Michaelknight]

So who do I contact to get a re-flash?

 

[kennythewelder]

Well,http://blackbearperformance.com can do it. Your local dyno shop can do it. You can buy a speed programmer, you can get a flash tuner like I have a Jet tuner and it can do it. Jet also makes a 2 CD disc set that can do it. Here is a pic of my flash programmer.

 

[Michaelknight]

And it worked for the 97 pcm? I just input my tires and ratio?