For the first item: if you are running that high an RPM at 20 mph, you most certainly have a clutch problem.
look at the video below. Your Polaris works very similar. The front part is a variator the 2nd part is the secondary. One of them is not working correctly.
for the 2nd: you are either fuel injected or you are carbureted. If you have a carburetor, you don’t have a TPS. If you are fuel injected, you have a TPS attached to a throttle body. What is your current setup?
for the throttle switch, take the throttle cover off and look at the setup and what happens with the contacts as you add slack to the cable. Then adjust the cable to just past where the contacts separate.
https://m.youtube.com/watch?v=pptnRGTH_XA