99 F250 SD acting up

My speedometer is erratic, not reading correctly, and the trans is not shifting right. It gets up to 3000 RPM and I have to back off the throttle to make it shift to 2nd. Then after driving a while everything starts working right. Next time I drive the truck it does the same thing. Any ideas?

I believe the speed sensor is on the top of the rear differential. It probably has something stuck on it or it needs replaced. If shifting and speedo related almost 100% it has something to do with a speed sensor.

Thanks for the help. Too cold to change it right now but when I do I'll post where it worked or not.