Adjust frig to make colder

How hot is it during the day. I do not know where the adjustment would be at on that fridge. It appears you are familiar with all the normal stuff seeing as you have been around here sense 2004.

What make and model of fridge? If it's a Dometic I have personal experience with your issue.

There is NOT an adjustment tab on fins in back of fridge.
You make adjustments on the upper control panel.

(There is a 'thermistor' on far right fin inside food compartment for temp sensing. Repositioning it ONLY works on fridges with AUTO Temp Control ----- fridges w/o adjustments)

Fridge in slideout SHOULD have fan(s) installed in outside compartment to enhance air flow thru the absorber tubes (slanted heavy tubing) and across condenser fins (finned unit at top)

Remove upper vent and look down...should be able to see fan(s) centerline mid-position of fridge.

IF RV MFG. bothered to follow fridge mfg. installation instructions/recommendations.

Majority of 'cooling issues' are due to improper clearances (too much clearance), lack of baffles (to decrease clearances & direct air flow) and not installing fans when in a slideout to help 'draft'

Installation instructions are available on line.

Having enough air flow in a slide is critical. Remove both outside vent covers and see it this helps. Also check that the fans on the back of the unit are running. As a test, put a box fan in front of the lower vent and see if this additional air helps it cool better.
If there is a dead air space above the top of the top vent then they did a poor job of installing. A baffle at a 45 degree angle sealing off this area will help the air flow.