Recently on several occasions i've suffered power loss under load, usually when driving up hill, at speed on full or nearly full throttle. Most recently i was towing a considerable load when i lost all power. Symptoms are power loss leaving car feeling dead/lifeless, this happens even when dropping down a gear, car seemingly refuses to "boost" and wont rev over 2-2.5K under load, yet dip clutch to remove load and it revs freely. Symptoms sometimes clear whilst driving after 10 or so mins, but more often need engine to be turned off to clear the fault. Any ideas what's causing this???