Moksha Yoga vs. Bikram Yoga

I started doing Moksha yoga July 9th.  I have been doing around 4 times a week.  I have been doing it to replace Bikram which is difficult to get to since it is not near my house anymore.  I love Bikram it just is so hard to get to since my studio moved.  Moksha is similiar to Bikram (as if it were a first cousin) but there is a lot of upper body work to it that I am not used to. I feel very weak in my upper body especially in Downward Facing Dog.  I also feel weak in the  lounges and warrior poses.  The poses I am used to doing in Bikram seem to come by sooner and last only a short amount of time.   I am committed to Moksha for now because it is near me and the studio seems to be a lovely.  I am committed to work on my upper body strength in Downward Facing Dog.  I am also going to try to do Iyengar to keep my posture good.