1996 SL2: no idea whats going on

I’ve been lurking around here for a while to find info on taking care of my Saturn, but I cannot find anything that pertains to my current situation…

So I drive a 1996 SL2 with an automatic trans and the other day I’m driving back to my house on the freeway and the radio goes off and comes right back on a couple of times during the ten mile trip. A couple of hours later I’m leaving my house and when I’m a few blocks away the radio goes on and off again but this time the car stalls for a split second too. As I’m driving away I notice my car won’t go out of first gear so I turn around and head back home. I begin to accelerate through the gears but then the radio goes on and off again and the car stalls and I once again only have first gear. I drive it around my block a couple of times and nothing else happens and I continue to only have first gear. As I put it into reverse to back it up into my parking spot in my driveway, there is a very large clunk coming from under the hood. I shift it out of and back into reverse and it once again makes the clunk. As I park it I leave it in neutral with the e brake up and pop the hood and have someone shift it into reverse. Watching the engine as it is shifted into reverse, it shakes as though some engine mounts may be busted and produces the clunking noise. About 8 hours later I take it out to drive it around the neighborhood and nothing seems wrong as it shifts gears or when you put it into reverse and the engine no longer jumps around or makes the noise.

Anybody have any idea what could be going on?

Check your alternator. These cars and transmissions are VERY VERY sensitive to voltage levels.

http://www.youtube.com/results?search_type=search_playlists&search_query=saturn+in+car+alternator+testing&uni=1

Also when was the last time you changed the tranny fluid and filter? Should be every 15k-20k.