F-250 B4 30mph it !!ShAkEs!!

i have a F-250 super duty and lately ive been having problems but i dont no what it is... when im at a light i start to accelerate and the hole truck starts to shake and as soo i pass 30mph the shaking stops and every thing is fine. . . I dont no if its the transmisoon or the fule injecteres... on a 150 i no it would usealy be the spark plugs, bujt in this case theres no plugs...