I have a 99 f150 auto 4x4 that vibrates when slowly accelerating around 40-50. This vibration is very noticable the whole front end of the truck hops and it happens for short durations and multiple times. It also happens when accelerating from a stop light but it is very subtle as if it's the road causing the vibration. I was thinking maybe a misfire? I'm going to check my motor mounts tonight, what could this be?