I have a 98 Durango 5.2 4x4... I replaced the heater core back in November and have been sitting on this problem for a while. when I put everything back together, I noticed the speedometer jumps to 40mph when I just turn the key on or idle. The needles rises when I gain speed but it does very slowly... when I do 25mph, it reads 45mph... when I do 45mph, it reads 53mph... and it eventually meets around 60 or 65... Is there anyway to reset anything or do i need a new cluster? hoping it might be possible to just replace a wire inside somehow instead of pay around $200 for a new one. I have been driving with a good sense of how fast I'm going but I'm going back to school soon and don't want to raise my chances of getting a ticket... thanks