Mitsubishi L200 intermittent power loss no dash lights

so a bit of a weird one. Driving well, no problems and suddenly the acceleration drops and if i keep my foot on the throttle it continues at that speed but if i ease off anytime, no additional power can be coaxed back. the car eventually stops, although the engine remains running. Put the car into Neutral so no load, the revs go up wen the throttle is pressed, put it back in drive and the revs dont so essentially the car doesant move, of if it does it does so in crawler mode. the engine continues to run and eventually the throttle starts to respond and i can drive off. problem is it keeps happening at junctions etc. had it in a garage and they have cleaned out a couple of pipes to the turbo and replacd the fuel filter but its still happening. no lights on dash and according to garage nothing showing through engine diagnostic checks/software. any thoughts on next steps