Mercedes diesel engine on my RV is powering out on hills.

YOU in UK and have a LORRY (means truck , in ROTW)
EDC 3776 electronics Diesel controller , engine lost power up a hill, sure.
No truck makers name?
no year truck
what size engine/? diesel?
lost power is :
1: bad fuel
2: filters dirty or packed up.
3: injectors clogged.
4: weak pumps.
5: other problems with EDC , scanned and seen,
6: truck needs service. or hill too tall./? IDK I can not see the hill.

Check your vacuum pump, that pump does all the switching of your sensor valves and ports. That would be my guess

is it a manual or auto?
if manual it could be the weak clutch. check for the diesel filters.otherwise its diesel pump need to be done.

No easy way, if you can get an electric pump, or a pump attachment for a power drill. Remove the fuel line, either at the fuel filter or the fuel rail, connect the pump with a bridging piece of hose, and let the pump do the work. Refill with a couple of gallons of petrol. Vehicle might smoke a little till all traces of diesel are gone. Diesel in petrol is not as bad as petrol in diesel. As you did not run the engine very little diesel will get up to the engine. Good Luck.

Actually a 2.8 diesel should be fairly weak on hills, especially if this is an automatic transmission.
You could check the fuel filter, or change to lower profile tires that give more power, but really turbo charging is the best way to really get lots of power out of such a small diesel.
Diesels not only have less hp then petrol engines, but also a narrower torque range.

http://www.turboglide.com.au/turbochargers/3ltrhilux.htm

Try or (have your mechanic) remove oil pressure switch and clean. They gum up and it's a safety feature that when car is in accident and/or roll over, when oil pressure drops (eng quits) power to fuel pump shuts off. Sticking oil pressure switch is common on Benz Diesels

If it is a cummins engine use Shell Rotella oil 15/40. This is what cummins recommends. Use the same if a mercedes engine. Black oil in a diesel is normal so don't worry.

diesel engines have loads of pulling power(towing/loaded)but you need to use the gears to keep the revs at peak torque.1st is a crawler gear(very low ratio).put car in 3rd going down steep hills saves the gearbox overheating.....

Hi most likely the EGR valve.

Thats an exhaust gas recycler vale, are you geting an engine light aswell?

does the car feel ver slow and stuggling with power and on hills. you can clean the EGR if thats the issue, or also the air mass sensor although you would be getting rough idle as well.

Please let me know if you need more info about the EGR.
Regards
Dan

Those old engines were made to last - compare the weight of the motor to one of similar capacity nowadays; the old ones were made of cast iron which is quite heavy, the newer ones like the C270CDi Mercedes motor weighs about 30-40%less due to aluminium parts. Longevity suffers, but you need less power to drive the engine, giving you more power to drive the car. Furthermore, the common rail injection used nowadays are a lot more flexible and powerful, due to the fact that the exact amount of diesel needed per cylinder stroke is injected, whereas the old system injected a fixed amount per stroke, whether you are doing 20mph or 80mph. So, it overfuels at low revs and underfuels at higher revs. To prevent it from burning too lean the engine has a rev limit, roughly where the mixture is running at "100%" effectivity. The newer motors use computers to make the decisions based on 83452 different inputs, the older ones just measured the diesel needed and the air supplied.

So, the sad news is that the only way to get the car to perform a lot better is to put in a new moter eg. C270CDi, or put in a REAL motor like a 350Chevy :-D but leave the 300D badge on and see the other guys $h@ their pants when this "diesel" smokes them!