Sorry to make a second related post, but I wanted to add more info to this problem to help diagnose it.
How do I know if my vehicle speed sensor or my computer is shot?
Occasionally when I am driving my speedo is kinda crazy, more so on the HUD than the analog. Sometimes when I drive it is fine, and other times it "jumps around" usually within 10 mph of what I am actually going. It affects my tranny and boost by shifting in and out of overdrive and I think it may also be killing my gas mileage. I was lookin in my book and it doesn't seem all that hard to change, but I don't want to waste the money or time if that is not the case. Also, is there only the one main computer on the TGPs, the one on the passenger side, or is there a seperate PCM I would have to worry about? Could this also have anything to do with my topgun 180 chip? The problem didn't start til after I put that in, but it was also a couple months and a bit of miles and 2 trips to the track on it before it started happening.

I went to take my car to school today and my speedometer wasn't working at all at first... so today I took the topgun 180 out and put the factory chip back in... the first 5 min of driving it was still acting up, but for about 15-20 min after that everything seemed to work perfect. Now I am not taking this as a fix cuz it didn't ALWAYS mess up before and it was still acting goofy the first 5 min of driving. I will take the car out again the next day or 2 for more testing. It seems kinda weird that the chip was causing this as a lot of people out there have the top gun series chips, but I suppose anything is possible right. I am really hoping that it's not the chip, cuz I love the performance it offers, but at the same time I don't wana spend $80 on a new VSS... I am at a loss here, any input or help would be greatly appreciated, cuz the car goes to storage soon and I want it fixed before I don't see it for 5 or 6 months...

hey bro, i have an automatic trans on my front lawn if you need a spare VSS.  might save the vaccuum modulator off it for a spare but the rest of it's going bye bye.

Must be something in the tune since there is another person having similar issues with an altered 8F chip in a L bod platform.
http://www.tgpforums.com/index.php/topic,5021.msg36321.html#new

well I drove it around a bit today and the speedometer stayed what seemed to be dead on the whole time, so I guess the problem was the chip, I am somewhat relieved to know what the problem was, but now that I have the old chip in my idle is a little weird again. When I am in drive at a stop light or something, the whole car rumbles and idles around 800, if I just touch the gas it's fine. I am going to do an idle relearn again later and see if that fixes it.