Good advice but at this point I don't feel strong enough to ride much in the middle ring. Down hill and flat I'm fine - small inclines I'm fine but if it's gets much more than that I have issues. A lot of the trails I've been riding are very rooty...to doing a big ring switch (which on my bike takes more effort and time) is not easy and a bit scary. I think I'm getting to the point I can think of 2 things at once but not much more.

Should I weight train to get stronger, or do rides where I intentionally ride harder gears to build strength, or practice practice practice the big ring changes??