Speedometer + Odometer Question

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diesel920

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Apr 26, 2021
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Location
East TN
So I need to tap into the knowledge vault here. 1998 k1500 z71 ECSB. Reman 5.7 vortec. Reman 4L60e. Manual transfer case. All stock + 33" tires and true duals with Flowmaster 40s and no cats.

I'm having some issues with the gauges.
The speedometer is quite a bit off. When the speedo shows 94, the GPS says 70 and the odometer is at 3200-3300. When the speedo shows 74, the GPS says 55 and the odometer is at 2500. I know the tires are bigger than stock but not by much so I don't think it would affect it that much. I also know that it is a gas hog but it gets really low mileage...13-14 mpg on the freeway.

Cruise control does not work. It has worked in the past for brief stints but shuts off while driving.

(Also the gas gauge is verrrry optimistic (always on full) but I'm assuming that is the pump/sending unit and unrelated.)

I know the cruise control and the VSS are on the same circuit so I was thinking about getting a new VSS to see if that helped the speedo and the cruise. Could that be the problem? Also I don't know what the RPM should be but that seems high to me. (it idles over 1,000). Is that high? Could that be related to this issue or does that seem separate? (IAC valve, vacuum leak, etc.)

I just wanted some direction before I start throwing parts at it.

Thanks for reading all that and thanks in advance for your help!
 
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