engine missing

This sounds more like a single cylinder spark plug or wire misfiring. As you put it under load (increasing MPH) the miss is becoming more noticeable and creating the stuttering feeling. Try a tune-up with plugs and wires before you tear the timing belt apart, a much larger and more expensive job.

The out insulation on the wires connection the coils on the top of the engine degrade. With mine replacement of the insulation solved the miss fires and stuttering, although mine was only stuttering under hard acceleration when I fixed it.