With respect to A/C systems, I have installed the Vintage Air system and the Tom's Bronco under-dash system. I like the compressor mount and hose layout of Tom's system better than VA's setup, and I have been able to get much lower outlet air temps from Tom's system than VA. With the VA kit in my '75, if I set the thermostat to a point where the outlet air temp is below 60 deg., the expansion valve freezes and it no longer cools (i.e. the vent temps rise to 80-90 deg. and stay there until the system cycles off long enough to unfreeze. I have replaced the drier (thinking moisture in the system was freezing the expansion valve) and vacuumed it out several times (even using a heat gun on the lines/drier while under vacuum to get moisture out), but I cannot get air temp below 60 when the truck is moving without freezing it up. I can easily get the outlet temp on the Tom's unit down to 39-40 deg., even with the fan on lowest speed. The VA unit seems to have a stronger fan, and it gives you better defrost than the OE Bronco (which you keep in operation with the Tom's under dash kit).
IMO if you do not live in an area where defog/defrosting your windshield is problematic, the Tom's unit WILL cool your truck better than the VA unit. It is also cheaper, but the under dash install is not pretty and will not work with some floor shift M/T's. The VA unit will do more in hot/moist/cold climates than an under dash system, but I seriously doubt that it would keep ANY truck cool in the southwest - it's basically a poor design that over cools the evap/expansion valve until it freezes, causing failure. I have not experimented with under or over charging it, but it may work slightly better if its overcharged (you're on your own if you go down this road) - if the low side was at 30-40 psi and you could keep the high side below 230-240 psi, maybe the added low side pressure would let you get a couple of degrees lower air temp before freezing.....