Odometer Not Even Close

[justagoodolboy]

My truck's interior is not finished yet so I don't drive it much but it seemed to me that the miles were not adding up on the odometer very fast but I didn't give it much thought till I checked it with my gps. I wrote down my mileage and drove into town. My gps said I went 5.1 miles and my truck said 2.2. My speedometer is 4 MPH slow- It makes no difference whether I drive 10 or 60 i'm going 4 MPH faster than it's showing, but that won't throw my odometer off that far will it? I tried using the search but couldn't find anything and I don't know how these odometers work- can someone please help me out here?

BTW, my guages are rebuilt white face ones from the guy on ebay. I don't know what it was like before I tore my truck apart-I never checked.

My truck is a 72 Chevy 4x4 3.73 350/350 on 15x8 ralley wheels 31x11.50's