Assuming you're handy with tools, it should be fairly easy. Are you sure its the TCC solenoid? My problem was that it wouldn't lock in at less rpms when it was supposed to, mainly at about 50 mph, and then it would slip back & forth in rpms until the OD light came on, and I was stuck running high rpms to do the same high speed. I could reset everything by disconnecting the battery, but it got worse over the months and the TC kept setting off the OD light more frequently.
Get the right replacement solenoid from Ford. Get a new transmission filter/screen & the pan gasket (usually available as a kit)--I suppose this is not REQUIRED but since you're down there, you might as well use a new kit. Also have about 3-5 quarts of new trans fluid to replace the old stuff.
You'll need to drop the front driveshaft in order to remove the trans pan--disconnect the driveshaft at the u-joint in front, and carefully let the driveshaft hang (make sure to mark the shaft and the differential so that you'll know where to re-assemble). Also, the small vent tube will have to be bent/moved out of the way in order to remove the trans pan (remember where it was so you can move it back into place).
Remove the trans pan bolts and try not to spill too much fluid on yourself. Remove the pan carefully--you may have to slide it through some tight spots but if the driveshaft is hanging out of the way and the tube is moved, it WILL slide out. Once the pan is out, clean it up and remove the gunk from the magnet. Also, the pan will hold some more fluid so you're bound to spill more as you slide the pan out.
With the pan off, you'll see 4 small solenoids each connected by small wire leads with black plastic terminals on the bottom of the trans. The TCC solenoid is the one CLOSEST to the front of the vehicle (at least on mine it was anyway--I don't think the 99 sports are too different). You can check at this point whether the new solenoid looks like the one on the trans. CAREFULLY disconnect the wire leads to the TCC solenoid. Then remove the bolt holding the TCC SOLENOID's bracket. Then remove the bolt holding the END (just the one on the end is necessary) of the metal retaining bracket. Once the end of the retaining bracket is loose, you can pull down on it to pull the solenoid clear.
Compare the old solenoid with its replacement. MY new one was slightly different in that it had some small red screens over the holes--I assume this is an engineering improvement over the old solenoid. Also, the problem with the old TCC will be obvious once you inspect the end of it and see how it allows fluid to pass through the worn out end. Put new solenoid in and re-assemble everything.
Be sure to use the new o-rings on the new trans filter/screen--one bolt holds the filter in place. And watch how much you torque the pan bolts when tightening. Bend vent tube back into place; re-assemble front driveshaft, noting that your marks line up.
I started with 3 qts of trans fluid, and then used more until it was full again. Take it easy when starting out again on a test drive to ensure you have enough fluid. Check it often, then take it out on the highway to see if the TC locks properly.
A fairly easy job if you're the handy type, and if indeed it's your TCC solenoid.
