Not sure why this happens to you when your car is cold.
I finally looked at the speed sensor yesterday. I took it out and decided to swap it with another one that I have. There is a crack in the mounting part of the housing. So then I take a test drive to Starbucks and no speedo reading... I go back home after there and take the second one out and look at both the speed sensors... I take them apart and inspect them closely.
I reassemble the three pieces that makeup the speed sensor and reinstall it. Go for a test drive around the block and now it is all good