This damn speedo...

The speedo is driven by a gear on the differential, so... Yes, it could be related. I had the differential in an auto go on me - the center shaft (pinion shaft?) slid out of one side of the differential housing, swung around and ejected the speedo gear from the tranny. I was driving along doing about 60 mph and I hear this POP and my speedo drops to 0. :?
On the other hand, it could purely be a problem with your speedo and/or cable - the VSS is part of the gauge cluster.

Well it's weird, I replaced the cable and it's been fine for a week or so, but all of a sudden I'm getting the check light again and it's bouncing at low speed.

could be related to the mount issue... if the engine is rocking, it could have loosened the cable in the tranny, so it doesn't have a good connection <shrug>

Shouldn't the clip hold it in? I probably installed that wrong too...

I would think so, but if it jerked enough, it could have come loose/broken

I was wrong, I assumed it was the VSS, but it's code 43. I thought that was O2 sensor, but apparently it's fuel supply system?
Then I look at the troubleshooting for it and it's O2 sensor after all! Something must have come undone when I was moving stuff around/washing the bay.

Code 43???
what ECU Are you running?

P28. After working with Crome last night, putting in a modified map etc, there is no CEL.