my 2002 2500D pick up runs hot when under load at the top of gauge, I am not thrashing it 45-55mph, up hills hot down hills normal. Nuns put a new engine in 5000 miles ago & truck as only done 55000 miles from new, what do you think.

 

Sounds like not a big enough radiator. You say they put a new engine in it. If it was a rebuilt engine they bored the cylinders. That makes the cylinder walls thinner thus transfering heat quicker into the cooling system which requires a bigger radiator. The radiator can't keep up so it runs hotter.I run into that a lot.
That is one possibility,there are more. An antifreeze mixture over 50/50 water/antifreeze can do that. Add waterwetter additive. A lean fuel mixture can make one run hotter ( doubt its the case) An overheating transmission can cause it( put an external oil cooler on it) (also external transmission filters routed to the front of the radiator work awsome,basicly an engine oil filter) A failing waterpump impellor can cause it or a restricted radiator. Fan clutch starting to fail.
I'm betting on the transmission overheating myself but it could be a number of things.

 

They have just had the gearbox out it had a lot of oil leaks could they have left something off. I am still taking it back after they broke things & left engine mounts missing bolt fwd not conected you name it.

 

I think i would take it to another shop and have them look it over closely before taking it back to them.

 

Yip fan not working do you now where I can get one