I have a 94 pickup with 22re and 5 speed. Today I was driving down a gravel road about 60 mph, and encountered a stretch where a tractor left his tracks imprinted in the road. Well, flying over those is very similar to rumble strips... and the truck was really BUZZING. That's when I noticed the tach and speedo wavering quite badly. Soon as I drove left or right of the tractor tracks, they were normal again. Does this sound like a cluster problem, or a common ground? The rest of the gauges seem fine, OP, fuel, batt, temp... all were solid. I'd think since both are affected at the same time, It's a ground problem?