tranny slipps in drive

A transmission slipping is not a good sign. You could decide to change the fluid and filter at this point in its life. When was the last time the fluid was changed? Did you check the fluid level, is it low? If Black, it should be bright red in color. Mind you, a fluid change is the last ditch effort to see if you can a few more miles out of the transmission before you have to replace or rebuild it. On a 98 Ford, you are way overdue for a rebuild, consider yourself lucky you go the vehicle this far.