I think it is fairly common or at least not unexpected.
Freezer ice packs can help the fridge keep up.
Some Dometic fridges have a Thermistor clipped onto the cooling fins in the fridge. Moving the thermistor up higher on the fin can help make the fridge colder.
Thermistors can also fail: http://www.classbforum.com/phpBB2/vi....php?f=9&t=595
I had a fridge with the opposite problem - it was too cold. The fix was replacing the thermistor after checking the ohms.