After a cold start, the check engine light will turn on when I first start moving. The scanmaster shows it as the vehicle speed sensor. After driving for a few seconds, the light turns off and the speedometer accurately works with or without the light on. This happens 95% of the time. If I start it after the car's been running, it might do this 50% of the time.

I replaced the sensor and that did not fix the problem. I checked the wires for continuity and there was continuity. I'm not sure what's left in the equation here.

A little history: after my engine swap, there were a handful of times where I was accelerating and the speedo needle would freeze for a second or two, then snap to where it should be. That was during the first month or two after the swap, June and July. It's been throwing the check engine light since August or September.