I have a 2005 d22 sport. in 1st 2nd and 3rd gear it pulls like a train as soon as i drop into 4th gear it holds back and struggles, if i send it forward into 5th gear its off and pulling like a train and only does this wen the vehicle is warm. i have tried a new fuel filter and injector cleaner and it has made no difference to the fault. can anybody shine any light on this for me please, thanks