Quite possible, although they were both fleet vans (mine was BT his was Royal Mail), I've maintained my engine quite well (another oil/filters change is due actually), where as he is overdue an oil/filters change by about 2 years. A lot of that is because the Ford 1.8D is bullet proof. The van will fail before the engine.
Sticking it in high gear and using full throttle doesn't labour the engine quite the same way. It just puts extra load on the clutch. Your engine wants to spin, the gears won't let it. Ideally you want weight based loads using lower gears. I'm getting 50MPH in a very hilly environment. The neighbour is only getting 40MPH. Ford claim it can get 55-60MPH. So I'm more than happy with 50.
That is because a lot of them are tuned to run rich when on boost. So you get a lot of unburnt fuel, unlike on a petrol engine where most of the unburnt fuel can combust on the way out of the exhaust, diesel engines don't have the same luxury.
My diesel runs stupidly clean, the only overfueling comes when I fire it up.