Juddering Grand C-Max, 1.6 (115) Diesel, Manual, 13/13, Zetec

2013 model on 13 plate (3 years old), 13,500 miles.
Good fuel used (not supermarket), full ford service history. On a 30 mile commute each day, I at least
once get a judder through the accelerator pedal and the rev needle flickers up to an additional 1000rpm for just a few seconds simultaneously. This usually happens just prior or after
changing gears mostly 4th, 5th and 6th (normal acceleration, not being thrashed). Taken to Ford garage twice, they plug in ECU and cannot find anything wrong. Warranty runs out in 6 months, don't want problem to worsen and then get a huge out of warranty bill. Worried also that the juddering will happen when overtaking or pulling out onto a slip lane, as although there is no loss of power when this occurs, it does not pick up speed either. If anyone can assist, please reply. Many thanks.