Windshield wipers not working properly

First thing would be to check both wiper fuses. As you say the motor works on high, but the washers don't work. Check the washer fuse in the box under the hood. If that fuse is good the problem is either the wiper motor or the multifunction switch that controls the wiper drive, specifically the Gray or Pink wires that control the lower speeds and the washer. Testing for which one is the problem will require a simple test light, some liquid electrical tape and access to the wiper motor connector out under the cowl.

To get to the motor you need to remove the wiper arms first. For that you pop up the plastic cover on the bottom of the arm and you will find a nut. Use a couple pieces of tape to mark the location of the wipers with them fully parked. If they won't park properly you can skip this step and once you repair the switch or motor you can align them when you are done. Remove the nut and give the arm a gentle tap or two on the metal part above the nut and it should pop free. Make a note as to which side is which. Gently remove the washer hoses from the small fittings on the vehicle. They a very easy to break off!
Now with the arms off you can remove the air inlet grill by removing the 4 screws/bolts that hold it as well as the reinforcement bolts. Now you can see the motor and wiring. First try unplugging the wiring and plugging it back in, A dirty connection is always possible. Any change when you try the wipers? Yes- spray the connection with some contact cleaner and unplug/plug it a few times and see if it works.
No - Take the test light and turn the wipers on Low. Now go to the connector and look for the Pink wire and the Gray wire. With the test light connected to a good ground push the tip into the insulation on the Gray wire so it connects the wire inside. The light should light up if there is no problem with the motor. Now do the same with the Pink wire. If the wiring is good to the switch and the switch is OK the light should light. If you have someone try the washers it should light up as bright as it did on the Gray wire. If you get the light at both wires you can now take the liquid tape and put a bit over each hole you just made. That will keep moisture out and keep the wires from corroding off. Then you can replace the wiper motor as it is faulty. If you get a light when on the Gray wire but no light on the Pink when you select any position or wash then it is likely the interior switch.

The outside wiper motors do have a lot of failures on the control boards so hopefully that is the problem as it is far easier to change the motor than the interior switch.
To change the motor you are almost there with it taken apart for testing. You would now remove the wiring connector, then remove the two bolts that hold the wiper transmission to the truck. Now you use a pry tool to pop the ball socket free from the arm. They show a special tool but it will pry off. Then the 2 bolts that hold the motor in place. Install the replacement motor, pop the socket back together, and reinstall it. Now plug it in and wrap a piece of tape around one of the wiper drive studs. Test the new motor on all speeds and wash. Be 100% sure it is turning the correct direction the wipers need to move to wipe the glass. Then be sure it stops and parks. Now you can reinstall the reinforcement and the air inlet. Try the motor again, Shut it off and let it park. Now install the wiper arms back on and tighten the nuts down to 22 ft lbs. Before they are fully tight try wiggling them up and down on the glass to get the splines to seat into the old locations, then tighten them real good. Now just to be sure, flip the wiper arms up and lock them, then test the movement again. If they look good flip the wipers back down (now is a good time to change the refills or wipe them off).

If on the other hand it is the interior switch, It's a little more complicated as you need to remove the trim covers from the steering column and under the dash, Remove the air bag SIR fuse so they don't deploy by accident, then go to the steering column wiring harness and remove the two connectors for the switch, then remove the switch. The wiper switch is serviced with the turn signal/dimmer/cruise control multifunction switch. Now you reverse the process to put the new one in. Be sure the sleeve from the old harness gets placed on the new wiring or you can damage the wires when you tilt the steering wheel.