Help nedded for ML270cdi loss of power
 

Since the last week my ML270cdi, 2001, 93.000Km have a loss of power. After a normal start, warming up, during a variable time it runs excelent in aceleration and speed, after a while the engine loss his power the speed goes under 130Km/H and rpm fall under 2500. No warning lights on.
I checked fuel filter, air filter, catalitic converter, intake air valve, exhaust valve, turbo and electric fuses, everything works perfect.
Can somebody drop a sugestion ? Computer analisis is far away from home.
Where can I get a Service Manual??
Where can I find the fuse F28/8, 7.5A for the Diesel Engine Control Unit?? It is not in the fuse box.
All the best,
Argenjagd