Problem with Mitsubishi L200

[chriz1]

Driving home in my mates L200 today and at 60mph all of the sudden the engine light came on and the truck lost all power it would do about 50mph on the flat,flat out but when it came to any sort of incline this reduced to 40mph wouldnt go no faster even dropping a few gears?
idles fine and no black some out the back..
Havent got my diagnostic tool with me at the mo
Any ideas?
what are the common issues with these?

[Dunclane]

We also have this problem with our L200. When the engine is switched off then re-started it goes away. I would be grateful if you could pass on any suggestions.