Speedometer too fast RESOLVED

[CodyZ71]

My trucks speedometer read about 12-15mph too fast at 60mph it would read about 78. I checked every ground, wires, connection, replaced entire cluster with a 120mph unit and it still was the same with no resolve. I went to the junkyard and grabbed another gauge cluster out of a 98 suburban and turned on my phones gps and it is now 99% accurate. So if your trucks speedo is off the only solution is to replace the entire cluster. Its easy to swap your odometer into the new one.
Hope this helps.

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[98chevy2500SS]

Had this happen to my 98 when I first bought it. It would read about the same as yours. Replaced the cluster and worked like it should. It's odd, I wonder why these clusters do that.

 

[CodyZ71]

Had this happen to my 98 when I first bought it. It would read about the same as yours. Replaced the cluster and worked like it should. It's odd, I wonder why these clusters do that.

I would like to know as well, it has to be something on the board itself because on my 120mph cluster I even replaced the aircore motor with a NOS GM one. On my original one I am not entirely sure when it failed, I did notice over the years I started complaining of people passing me while I was doing 65mph in a 55.. so I guess I was going about 48 lol
I've owned the truck over 16 years and it was always kept up above average so idk