Help! Speedometer going nuts!

A few months back I had 4.10s installed on my 2002 GT along with the DM SpeedCal. Had no problems whatsoever. Yesterday I picked up the XCal2 from Dallas Mustang where they threw on a mild tune for me (will be dyno tuning after my cams install). Took the tuner home and flashed the computer....Everything seemed fine, except that my gears were being compensated for twice, so after confirming the tune was good, I removed the SpeedCal. Drove the car a while and everything seemed fine. Speedo was reading properly and everything. Next morning, my speedo is going crazy. After I hit about 25 mph, it starts bouncing all over the place, usually oscillating around +/- 10 mph, but sometimes briefly dropping close to 0, even at highway speeds.

I tried flashing the stock tune back on, but it didn't make any difference, the speedo was still doing the same thing. I haven't tried reinstalling the SpeedCal, and I really don't want to, but if it'll solve my problem I'll do it.

Any help here would be greatly appreciated...It's driving me nuts.

Jason, you just follow the SpeedCal install instructions backward (available on Dallas Mustang's website). I didn't do my install, but uninstalling it was relatively simple, though I'm obviously having issues.

UPDATE:
Well, we plugged my SpeedCal back in tonight and we're noticing some interesting patterns. Without the SpeedCal, the speedometer reads correctly up to 25 mph; after 25 mph the speedometer goes nuts. With the SpeedCal, it reads 0 mph until I hit 25 mph, after which it reads correctly. (I set the SpeedCal to 1000000000, so it shouldn't be changing the reading.)

Does anyone have any idea why 25 mph seems to be a significant number and better yet why the SpeedCal is effecting anything? I'm totally out of ideas, but at least I know how fast I'm going as long as I'm going over 25.

Well, I finally broke down and bought a new VSS. I removed the SpeedCal and left my tune set to compensate for the 4.10s, and I now have a working speedometer.

I'd strongly suggest disconnecting your battery before messing with any part of this electrical system. I'm afraid that not doing that may have been what killed my sensor.