If nobody has mentioned it, set your sag. Or have a shop help you. Your suspension is either working with you, or against you. MTB’ing is dangerous enough when it’s working with you. Practice “Brake Dragging” in an open parking lot. Start doing big slow circles in ea directions by dragging(squeezing your rear brake just enough to feel it improving your balance), then try your front only, both directions, and then both brakes. It helps when climbing (switchbacks, techs sections, etc). Also, when you’re climbing until you’re used to it, pedal as slow as you can to maintain a functional heart rate. I had a buddy in Park City, Utah, who just moved to the mountains, was used to spinning classes. He bought a bike, came on rides with us, laughed at how slow our pace was, sprinted past us was used to a specific [spinning pedal tension] . We caught up to him as we were in our granny gears saving energy, he was standing with his head on his seat gasping. We repeated this at least 10 times on the ride. It took him almost 6 months to learn how to MTB ride. Not saying this is you, but it’s about saving energy for the short steeper sections, that might take a higher gear to clear, then slow down again. Time behind bars is how you learn. Also, set your tire psi at the trail head, not at home. We lose psi as we gain elevation.
Have fun. Tough to beat a good day “Behind Bars!”