1. check your tires for rips and tears, feel for bubbles on the side walls in and out, feel with your hands the surface of the tire tread to see if there might be a bubble or a tare/rip. that could be the problem. 2. could've driven on a bumpy road lately/or hit a decently sized pot hole to knock you tire balance off, go to your local tire shop and have them do a tire blanace/aliginment/rotation. that should take care of your problem. 3. it could be your rear end, mustangs v8's suffer from the legendary pinon & ring problem in the 8.8 gears. that is a costly fix so fix your tires first then if it countinue its eaither ur rearend or ball joints worn but not to the point of making noises when turning or you are suffering from a vacum leak somewhere, lastly it could be your catylack converter inside your transmission but i highly doubt that one because it only occurs at higher speeds and gets worse as speed increases.
If the rotors are warped it can cause a shake when you hit the brakes.
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.
Probably bad u-joints in the front. Had the same.
Normally this is a symptom of a tire out of balance. Have your tires balanced and this should solve the problem.
I would check your tires they could be out of balance. or a tire could be bad .
sounds like you need a wheel balance
50 mph is 31.07 kph.
Tire our of balance or bent wheel. Have your tires rotated and balanced.
50 kph = 31.07 mph
roughly 31 mph. the formula is (KM * 0.62)
could be an alignment issue or in my case a broken cv axle. i'd say take it to a shop and they should be able to answer your issue