Need more info. Does just the engine run rough or does the steering shake or does the whole vehicle shake betwen 50 and 55 mph?
Normally this is caused by a tire out of balance or a bent wheel.
The symptom would indicate a wheel/tire/balance problem. You need to have a professional inspect if you are driving at those speeds. also make sure if you drive at 120+ mph, you have "Z" rated tires for safety.
My guess would be wheel balance.
there is certain mph's that do that. ur tires are prolly off balance or your alignment needs to be fixed.start off by balancing and rotating ur tires.and if it shakes when the brakes applied the you need to check your rotors.
About 638 mph
i would really like to know myself
It depends on the speed you are going. For instance, if you are going 4 mph, it would take 1 hour to go 4 miles. If you were going 8 mph, it would take 30 minutes to go 4 miles. If you were going 16 mph, it would take 15 minutes to go 4 miles.
If it happens when you are driving fast (60-70 MPH) it could be that your wheels are out of alignment.
Can be a bent wheel, tire out of balance, or worn suspension parts.