On the fridge, mine takes a solid 8 hours to get to operating temps. If it still won't cool on electric, have you tried switching to gas? That'll narrow down where the problem might be. On mine (1987 Norcold) there's two relays that only get used in electric mode. Cheap and easy to narrow further.
Question on the tires. You mentioned in the first post you replaced two tires. Then later mentioned it again. That mean two tires total? Or all four? Reason I ask is that trailer tires can look perfect but still be too old to use safely. I always replace them all at the same time unless one or two was damaged by a road hazard and I'm certain of the condition/age of the others. You don't want to spend all this time and money on a new trailer and have a blow out cause damage.
