ScottB

I have a 1990 4x4 pathfinder auto trans 249000 miles tires less than 2 months old, it vibrates and shakes badly when driving at steady speed 50 mph or faster if I hold speed steady, if I let up on the gas it stops shaking, and if I accelerate it stops shaking, but as soon as I hold speed steady again it starts shaking all over again. Anyone know what is the most likely problem. Thank you