Good thread and valuable information.
I have a couple thoughts and additions...
Moving the temp probe upwards on the evaporator should actually make the temp sensor read colder temps, which would have the opposite result. The evaporator temps are hotter at the bottom and colder at the top.
I believe what's happening is you're moving the temp probe to a spot that has better airflow because it's more inline with the fan. The increased airflow is what's keeping the temp probe reading a little warmer, which in turn keeps the compressor running at full and in turn making the outlet temps colder.
So my point is that this "mod" shouldn't really make that much difference as far as "moving the probe higher makes the AC output colder". I believe moving the temp probe to a spot that has a little better airflow is what you did. Moving the temp probe all the way to the very top "should" result in higher outlet temps in my opinion and assessment of the operation.
Here's MY suggestion if you guys want to REALLY get some cold AC air. Especially when you're talking about very high temps in your coaches, try this... Pull the inlet vent cover and filter off, pull the evap temp probe out of the core and let it hang in the inlet air. That should all take a total of 2 minutes and is totally reversible.
YIKES! What did he say to do? Won't my AC blow up? Won't it turn into a giant ice cube? Won't I void my warranty? To those fears I say this... Relax. Nothing horrible is going to happen. Your AC isn't going to blow up. It's possible that you could ice up the evap core, but it's not that likely unless you try to get your coach down to 60 degrees by running it for hours on end without it cycling. And if you're worrying about voiding a warranty, you probably shouldn't own an RV. lol.
I don't have my temp probe in the evap core. It's hanging in the intake air. I've ran my AC for hours on end without cycling, getting the coach down into the '60's on a hot day and it didn't freeze up. The kind of use most of you are complaining about poor cooling isn't the situation where evap icing is likely. Most of you want better cooling on super hot days or when the coach is super hot inside. If the inlet air going into the AC is 80-90 degrees, it's not going to ice up.
So try it. I guaranty you will get HUGELY NOTICEABLE cooler AC output temps. If it does ice up, you're gonna know because the outlet airflow will stop. Simply turn the AC off for awhile and it will melt. Not a big deal. Stick the temp probe back in the evap core and experiment over. No harm, no foul.