1997 Yukon slt 4wd speedo is off

[Jesse G]

I am running 265/75/16's which is the way when I bought it and of course the person that put them on, never adjusted the speedo. Is there a DIY fix I can do or do I have to take it to a tranny shop? Thanks

 

[SunlitComet]

changed in the pcm by atuning product or tech 2 scanner.