First you need to have the voltaged checked out,thats way too high, that will cook the battery's early. I agree its not going 8K, there are different settings on them, maybe your is on the wrong one say for a 6 cyl.motor. I believe there is a regulator on those rudes and it may be possible to do it yourself, I can't imagine it being too hard. If you feel adventurous to DIY, go to this site for the part
www.usavemarine.com, now I'm not sure if you can, so I'll give you a phone number ask for Mike- tell him where you came from- and he'll help 727 938 9796- actually ask him about the tach too while your at it.