You might try putting some old milk containers filled with water in both fridge and freezer to absorb the cold temp and hopefully stabilize the temp swings.
Here's my story on the 1200 Norcold I had. It never really did work great from the day we got the coach to the day the Norcold finally crapped out.
I added a small fan with snap disc on the back that would aid in blowing air across the back, can't say it made much of a difference.
I played with the thermistor, again, couldn't tell the difference.
I installed remote temp sensors in both the fridge and freezer and monitored continuously. If fridge started to warm up I'd transfer a frozen block from the fridge to keep the fridge in safe working temps.
I finally replaced with a Samsung RF18 residential. In order to remove the Norcold from the coach it was completely dismantled. I was surprised at how poorly the cooling unit on the back of the fridge was installed, large gap between it and the back of the fridge. No wonder it didn't work well.
My recommendation is notify the dealer you bought the fridge from and pursue a warranty claim. I'm sure they will try will push back but don't relent. Keep track off all correspondence, take you case all the way to Norcold.
If you don't get it fixed now it won't ever work right.
2002 Monaco Windsor 38 PKD
2005 Jeep Grand Cherokee w/5.7 Hemi