You may have 2 channels due to poor signals. The limit for 3-channel is 51dB for 64QAM (presumably ATDMA on your post). 2-channel is 54dB, and your ATDMA channel is close to that. 16QAM (TDMA?) allows 1dB higher (52/55).
That had happened to me. I was at those exact same upstream power levels and couldn't get more than two. Made some changes that lowered the power output and the third channel is there now consistently. -- I guess we'll have to sue Mother Nature now for voter suppression. Vote Romney/Ryan 2012 and end the stupidity.