The hills of Chequamegon surprise a lot of people. They think of the area as flat, and compared to Colorado it is. However, those short, punchy hills just keep coming one after another, and they take a toll on your legs. I am still a Chequamegon 40 newbie at 5 races, but my times have been steadily improving each year (just over 3:00 this year, and I am an old fart). The best advice I can give is to focus on endurance first, and hills and speed second. Once you can handle a sustained, hard effort for 2 to 4 hours, the hills won't seem as bad.
To build endurance, ride your bike. Ride it a lot. This will help to establish a strong base of endurance fitness in your legs. If you have a road, or gravel bike, ride that more than your MTB. Don't worry too much about finding hills - get miles into your legs. I try to do one long (50 to 100 miles) and one medium ride each weekend, with 2 or 4 shorter rides (15 to 30) during the week - depending on available time. Use this site to find some gravel in the SW area:
https://gravelmap.com/#@44.98780413470361,-93.77512616107026,9,hybridAs you build good endurance, you can add speed intervals, or hill work as desired. One hill drill I have used over the years is to find a small hill 100 to 200 in elevation, and 1/3 to 1/2 mile in length. Ride up the hill in your easiest gear (in the small front ring if you have a 2X), and then ride back to the bottom as a recovery. Shift the next hardest gear and climb it again. Keep doing this until you have gone through all 10 or 11 gears in the rear cassette. Do this once a week. You may not make all 10 gears at first, but over time, this will become an easy drill.
Good luck! See you next year in Hayward.
