i figured out my problem. i've known it for a while, but my last game confirmed it. my internet connection is just fast enough for me to get by in most games, but slow enough to get me killed.
for instance, i always lose melee battles because my latency is high enough that i miss the window that would put us into the "melee contest". so the host doesn't see my melee in time and i lose. same thing happens with shotguns, swords, snipers, and probably maulers.
so i'll need to upgrade my internet service if i want to play for real at all.