Welcome,nothing wrong with a good LB7:D.I love mine easy to work on and if your looking to mod there are a lot of parts for sale for them.Also they get the best milage of the dmax line up.:thumb:
I think he will need more fuel over stock,I believe he will be maxing everything out to reach 600 if he can get there on stock fuel and injectors.
Welcome to DD very nice to have you here and to help you with any info we can.:hello:
Most likely a bad stepper motor in the gauge cluster.Fill out your sig so we have info on your truck,what mods if any and where your from so we may help if we are close.