Dometic Refrigerator cooling issue

[Pocketlake1]

we have an AC/gas Dometic RM1350 SLMX (4 doors). works perfect on gas, and inconsistent on shore power. On this trip turned it on,brought it down to 36 degrees overnight, then loaded it with food, was good for a couple of days, came back from a day trip today, and it's at 60 degrees, using shore power. I know the power is good and clean. That's happened several times over the last few months. We've just moved it over to gas and fully expect it will get down to 36 degrees over the next several hours, perhaps overnight

Problem seemed to start last year when we experienced a low voltage problem, realized too late we were only getting 105 volts, and moved over to gas, but damage may have been done then

We went to Camping World, the technician (he is a good one) "knew what the problem is" and rescrewed some insulation panels that he felt had come loose and was blocking air flow. Everything seemed fine at the service center, good temps when running it overnight, so accepted as solved issue.

Then problem has inconsistently reoccurred, we can go for a few days with no issue at campgrounds, then temps go up at the next site. Traveling between sites it's fine since we're on gas. Only occurs when using shore power.

Someone in a post several months ago suggested changing the heating elements. I can't find a manual that clues me in on where to locate the elements (believe there are 2). Nothing on Dometic web site

If someone has some insight into that, or other suggestions, it would be appreciated, as we are baffled. Hope to avoid another trip to a service center, and the $150 charge to not be able to isolate the problem. They've had it a couple of times already, and so far I've found the Camping World extended warranty to be useless (along with their $300 deductible)
Thanks
Ken