I've got a problem
 

I've got a 99 TA. Something is draining my battery. If I leave the car sit for two or three days and try to start it, it won't even make a click. If I let the car idle for more than a half hour the battery is drained to about 8 volts. The car has had numerous new batteries and two new alternators. I've also noticed when i start the car all of the gauges jump all the way up and then come back down. Its never done that in the past. Any ideas?

have you tried a parasitic draw test?
disconnect the negative terminal from the battery and put an ammeter between them. wait about 5 or so minutes for all the computers to go to sleep and it should read around 50 milliamps. if it reads more than that start pulling fuses till you find the problem.

Your car should be charging at idle. Something must be telling the alternator not to put out at lower speeds. Not sure how that works but you should look into it from that angle. The alternator does get a "generator turn on" signal from the PCM.
http://chevythunder.com/19992002_ls1...m%20Schematics

The cluster issue is known for the '99 cars. Something about a memory chip not retaining it's info. Worse when cold and/or low battery conditions. There was a dealer TSB & fix but that was then. More here:
https://ls1tech.com/forums/general-m...ts-itself.html

I replaced the alternator last year and was haveing the same issue. I took it to the dealer and they had the car for a week. All they did was put another alternator in it. It ran fine for two days then I had the same problem.