BuddyO

I have a laundry list of problems and I'm hoping they all or most have a common cause. First, about two months ago my fuel gauge started acting up. It would go to empty when I knew it was full or it would just read wrong. Just the other day the "brakes need servicing" warning came on as well as the abs & brake lights on the instrument panel. Brakes work fine and the fluid level is at max. Yesterday, while going to work I was doing 60 mph with the cruise on when the trucks speed started to fluctuate up and down constantly. I took it out of cruise control and all that stopped. It was then that I noticed my speedometer needle was moving from 60 to 50 mph, back and forth, quickly. The rpm gauge remained pretty constant though. On my way home I was going 60 mph and the speedometer went from 60 to about 10-20 mph and I lost forward momentum like I was in neutral but the rpm's remained constant at about 1800. I rev'd the engine but nothing happened except an rpm rise. I was looking for a place to pull over when everything went back to normal, except for an occasional dip in speedometer indication. Does anyone have any idea what's going on? The instrument cluster malfunctioning wouldn't influence engine performance would it?