Cooling and alternator problems

84 trans am 305. car runs fine except the battery is always low around 11 or 12 volts, but when i drive on the highway it goes up to 14 or 15, then when i go back on slow roads it loses power again. is this the alternator or is the fan belt too lose? also my coolant gets kinda hot, usually at or above 220. Ive already flushed the coolant, but it is always really rusty. Where is the rust coming from and is that the reason why it is running hot? I really dont like the cooling system for these cars, had a problem with my 88 V6 Camaro too. Hasnt overheated yet, but i dont want to run into that problem before i can get it fixed. any recomendations on fixing these problems?

If your cooling system was neglected in the past, there is probably lots of accumulated rust and scale breaking loose and contaminating the coolant. A reverse flush with a good flushing compound would help.
As for the battery and the temp, don't trust those cute little factory gauges. They are not too accurate. Get a good digital multi meter. The battery, with the engine off should have about 12 volts. With the engine running, it should read about 13.7 to 14.5 volts at idle, with no accessories or electrical stuff on.
Sometimes headlights etc can draw more power from the alternator than it can provide at idle. This is normal. But if you must rev the engine to get more than 12 volts with no electrical stuff switched on, your alternator may be faulty.

thanks, i just tightened the alternator belt and i think that may have fixed it. i was thinking earlier that the rust may be coming from the water pump, is that possible? i think i should replace some of these parts because i know that water pumps usually are one of the first things to go bad. ive replaced the thermostat and it helped a little bit, but im almost certain that the coolant is getting too hot because of all the rust. one last thing, could you describe how you reverse flush the coolant?