Evening All......Advise needed

I am new to the forum.........be gentle.....I have a defender 90 TD5 with 124K (or near enough) and when accelerating towards the high end of the rev range in a few gears, the engine seems to stutter a bit. If I am gentle on the throttle it will go through this but if hard on throttle stutters more...any suggestions ?
It has just been dropped off for a major service and MOT and I have explained to a garage that has huge landy experience as they service defenders for the army and UN....lots of nice toys in their yard inc tanks and other big stuff.....looking forward to your thoughts....Cheers !

Pay the bill and then read the invoice to see what the problem was. Voila.

Dirty maf, dirty fuel, suspect fuel pump, oil in injector harness to ecu, take your pick

quite possibly over boosting, if some one has shortened the turbo actuator arm them it produces more boost than the ecu is set for, so the ecu cuts fuel, once boost lessens fuel is restored