Why1998 Dakota, 4x4, 5.2L, auto, 126K miles have rumble strip sound when lightly accelerating at highway speeds?

 

Bad u-joints?

 

Ran over rumble strips?

 

If it doesn't happen at low speeds, it almost sounds like lugging. If it happens at speeds 45 and under, it might be a lump on one tire. Otherwise, could just be the sound of the cylinders firing after torque converter lockup. In my truck I get a definitive sound after lockup since the engine is able to transfer all sympathetic vibrations, which almost sounds like a rumble strip. Although it goes away after about 55 or 60 mph when it's producing enough power. Other options would include an exhause leak. It depends on if it's just a sound, or if you can actually feel it in the steering.