Hi Pete, Surely the engine is out of balance, so this indicates one or more cilinders not working in tact. So, as you suggest maybe a fuel injector. In gears 1 and two no problems. From 3 to5th increasing problems. The frequency of the motor trembling is around 4 times a second or more. And as i mentioned , in 5th it also trembles when i have the gas pedal in a fixed position, i.e. not accelerating. How could you test the injectors then?