Your pressures sound good and with a pressure difference like that, your expansion valve is probably okay, if it goes bad it will not act as an orifice, thus producing a pressure drop.

I still think that with pressures such as this, the a/c portion itself is not the problem, the problem will be related to air flow across the evaporator. I'm sorry that I don't know more about your particular chassis to offer more detailed advice.

Keep checking those duct doors and such,

Good luck,