wireless connector problems

Not sure if this is the right place, but.
I am connected to my internet cable modem via a d-link DWA-125 wireless connector. It works great, get 35+ Mbps usually. However, during PM peak I only get 0.5 to 2 Mbps. When I run a ethernet cable from modem to computer I get 35+ speed. Would a powerline adapter make a difference? Would changing the channel on the adapter make a difference? And why does this happen in the first place! The house set up doesn't allow me to permanently use ethernet cable, more's the pity.
Hoping some one can enlighten me.
Old dog