2000 JGC vibration

My 2000 JGC vibrates at 50 mph and continues till 60 mph then smooths out. It only does it with normal acceleration. Does not occur while coasting or rapid acceleration. I have noticed it has more to do with what rpm's I am at (1500). Any advice?

With the rpms as a focal point I would say that you may have plugs breaking down. At that speed normal accel you should be in overdrive. That is a good load to bring out bad plug wires.
A tire out of balance could viberate at certain speeds and u joints could do the same. But I would think you would connect that to rpms.
A scan tool may show if there has been any misfires. Not all misfires will set a check engine light.