During hot weather it acts like it runs out of gas when the tank is under 1/2 full, if you fill the tank back up runs great,

Well the fuel pump is cooled and lubed by the gas in the tank, however it only takes about 1-2 gallons to do that, but there may be a remote chance the fuel pump is failing, you can get the fuel pressure checked, if it's out of spec replace it. You don't mention any trouble codes or check engine light being on, so i don't think this will have anything to do with the EVAP system. Get the fuel pressure tested (you can buy the gauge as it's fairly cheap, or rent/borrow one from most auto parts stores) and proceed from there.

I've got a 2004 montana this winter it showed classic symptoms of a bad fuel pump. Replaced the pump and discovered corrosion on the fuel pump electrical harnesses that are located at about the driver door/slider and underneath the van by maybe 4 inches. Occassionally mine will die out and wont restart (fuel pump prime is also absent) unless the outer harness(3total in that cluster) is disconnected and reconnected and like magic it fires right back up as normal! Just thought I'd mention this and maybe spare someone the hassle of having to drain & drop the tank for an issue that potentially doesn't exist at the pump itself!