do these have grease in them I can clean and replace?

that's the only reason I can think that it does this.

Mine has given me grief in the cold, but that was really COLD, like - 30 deg. C. It would hit the peg (160 km/h) while driving at 30 km/h for a few blocks, until it warmed up a bit, then it was OK.

 

I notice it is kind of sluggish around 100 km/h, which sucks, as it means I don't really know how fast I am going. I notice the tach shows more variation than the speedo, and I am pretty sure the tach is accurate.

 

Greasing the cables is possible, but not recommended, as the grease can migrate up the cable into the speedo, where it is not a good thing to have.

Mine does the opposite reads zero if its under freezing and will intermittently react.

Maybe the cable is partially pulled out? Check that it is properly screwed in at both ends. Can't hurt.

Yeah I did that last year.

But I did see a thread on subaruxt.com about gear oil riding a bad cable to the speedo.

Could have gear oil in it.... Maybe.

Check the condition of the cable, it may be tired at the transmission end and need replacement.