What causes a diesel to gain power while driving then lose it?
bad fuel, water in the sytem?
It could be a variety of things.... first and easiest explaination that comes to mind is that if you seem to gain power under load.. it could just be the natural way that the turbocharger works... the higher the RPM, the more exhaust gas leaves the combustion chambers and the more intake air it will suck in... making it have more power, your power gain is exponentially increased with higher RPMs than when idling
this could also be caused by a clogged air filter.
Could be the mass airflow sensor.