Toyota Previa 2003 diesel manual D4D - Loss of Power when Warm?

Hello guys, I have got a problem , my Toyota Previa D4D Diesel 2.0 manual, has a problem, Toyota has seen it twice, once charged me with nearly £800 to change something like "pump kit supply" (it says on the receipt) and drives the same.
When engine its cold, for about 3, 4 miles it pulls very well, as it should, now, as soon as it gets warm , its losing power, behaves like in LIMP mode, but its not in limp mode, no light show up , no computer pick s up any fault, but it becomes lazy when it gets warm,
Now , every now an then , on its own ,kicks in , and pulls hard but only like for a few seconds, and then it goes lazy again.
Please help.

Ps , a friend of mine disconnected the MAF sensor and EGR, drove like that for a few miles, no change. they seem to be fine.