Strange speedometer issues.

So now that its cold as hell outside my speedometer is acting up. Its a 92 with electronic speed sensor (new), and until the truck is thoroughly warmed up and driving around for a while the speedo jumps around a bit, about 5 mph, and is very inaccurate. I tightened up all the screws on the back of the cluster when I put a couple new gauges in a few months ago so I'm not convinced thats the problem. It doesn't ever stop working just fluctuates.

Is that the only possible culprit or is there something else that could cause it?