this morning i started up my truck and it started rough. it was about 15 degrees outside. when it started it started humming and i could feel the vibration in the steering wheel and pedals. it was a vibration like a cell phone. my anti lock brakes havent been working they just lock up and even skid on pavement if im not carefull. when i pushed the brake the vibration seemed to get worse. but as i reved it up it got worse untill about 1300 rpm. i drove it to school and it would only do it when i completley let off the pedal. when i got to school, about 10 miles, when i got there i shut it off and restarted it it quit but seemed to still be there a little bit. what could be wrong???
its a 1999 dodge cummins.