I've got a 97 power stroke just picked it up, clean truck no rust, 4x4 extended cab automatic. The speedometer will work but sometimes quits and when the speedo isn't working it shifts hard, but just when the speedo goes out, just wondering if it's a simple fix thanks!

 

The vehicle speed sensor on the top of the rear diff controls the speedometer, so that sound like the logical place to start. You can take it out and clean it off if it's dirty it can cause the speedometer to bounce the good news is it free to try but it will most likely will not fix your problem, it could also be bad but you will also need to check the wiring.