OOOOOk I finally got my truck back from the shop and don't even want to look at the bill. I havn't yet anyway my pa and ma payed for it sense it was a gift. Anyway my dad forgot to mention that I was having speedo trouble but don't want to take it back to the shop. Ok so heres the problem. At first it didn't do anything so I took out the whole cluster and checked all the wiring. Other that a few burnt bulbs everything looks fine. I did notice the foam seal that runs around some areas of the cluster have been falling apart. So just to be sure i went ahead and cleaned what I could. After that I went for a test drive and right away it started to working. But its like 25mph off!!! So I left it forawhile til I could get back to it. But it seems like it works when it wants to...or somewhat. Then suddenly it would stop working but when I push the reset button on the miles it will start working again. I also don't think the miles are acurate because if I go around the block (about half a mile) it will read around 2 miles??? Any thoughts? I think its an electrical problem but where do I start?

1993 Dodge d250 dually 2x4 5spd