Eng. Lt on. Shakes at 50 mph. Wont go any faster. Shakes like its missing a cyl

have the code checked. if you ran it too long, the cat converter may be damaged causing a restriction. you need to check compression, plugs, wires, injectors and vacuum leaks. Roy

Agree with Roy read codes first to see what is most likely long. Start with the basics hopefully its just a spark plug or coil problem but if the engine has higher mileage make sure the valve clearances have been checked, they are shim adjusted but are often over looked as part of regular maintainence.