AC and RPM

Please help....my 1998 sixbanger at 128,000 miles is starting to act up lately....first thing is that my RPMS dip low when I put the car in reverse(automatic) and feels like its getting boggy but does fine when it is in drive.....I thought it was the battery so I changed it the the optima red series and the problem is still there.....what could be the problem ???

Second problem is that my AC all of a sudden stopped blowing cold air while it is in park....what gives ???? The AC then blows nice cool air when I am driving on the highway but as soon as I get to red light on a regular street..... the hot air comes back againamnit:.....could it be that my freon is out??? If so, is it hard to recharge it my self and how??? Or should I just take it to a dealer????which is something I hate to do.....

I got the tranny fluid flushed and replaced at about 100,000 miles.....just now the radiator top hose to the engine just blew up and i replaced it but the thing overheats now within 15 mins....would you be able to tell me where the thermostat is or the sensor...I was told that the thermostat may be the problem...top hose is hot and bottom is cold....something is not letting the valve to open to drain i was told.....any help would be greatly appreciated....I hope its not the tranny....I am in college and I am just making it by with what i have so the possibility in going to a "stealership" to have it looked at is very low but i would like to do my own things first too see if I can fix it.....the dealer would be a last resort.....which I hope will not be too late.....

I replaced the thermostat but that was not the problem....it was the damn radiator fan the whole *#@$%## time!!! I did not know how much a radiator fan affects the whole car...AC,RPMS,water circulation......well, after a few bottles of antifreeze,a new thermostat and a new radiator fan...I finally got it....the sixbanger is back!!!!LOL!!!!