Ok......but, we're not attempting to get a whole cabin temperature...for the most part all of the tests done here have been for temps at/inside the vents. An overall cabin reading/test would also be interesting and I can see that for that all vents should be open....but not having the rears open for a specific front vent test should only help (or at least not affect) a temp reading at those vents.
That depends on what your intended goal is. If you're only concerned about the temperature coming out of the vents, sure. If you actually care about the internal cabin temp, then you're only testing one piece of the entire puzzle. If you're looking at an equivalent volume of air, with the same circulation patterns, then the temperature is relative.
In other words, if the AC can't cool the volume of the cab, no matter how low the temp is coming from the vents, then the system is inadequate. If you're disabling parts of the system to get a front vent temp result, then I find it difficult to then conclude that the system is deficient.
I have experienced a notable difference in the cooling ability at idle with the fan vs. driving the truck. I wonder if there's something that FCA can change to improve function at idle, or if it's a limitation in the cooling area of the condenser affected by the round fan vs. the entire rectangular area cooled as the truck moves forward.