I ain't watching your online matches, but I'll tell you what you do to win with Jam, online. Just run a lot of mixups: crossups, high/lows, tick throws, staggered blockstrings, etc. As long as you got your mega-damage combos down, you'll be straight. Jam is super frustrating to fight under delayed circumstances. Lag gives a heavy mixup character like Jam a lot leeway. Remember, you want to the other guy to worry about blocking under lag, not you. Get your offense going before the other guy and you'll win. The huge amount of mixups Jam can unleash in a short frame of time, coupled with her obscene damage, you'd have to be unbelievably predictable for someone to beat you with any sort of consistency.
I broke my word, I just watched part of one match, as much as I could bear. You're too predictable. You need more tools in your toolbox. You have not plateaued at all. You're not even on the mountain.
Go here for a bunch of #r vids: http://www.youtube.com/user/getterbeeeeeeeeeeem
Search with "紗夢" or "JA" to find the Jam vids. Watch the setups that they do. Can you imagine trying to block some of that stuff under lag? And they're being conservative. Online, feel free to overextend. And hitconfirming, I wouldn't worry too much about that. It's hard to do online. Grab your Nikes and just do it.
If this is practice for eventual offline play. I won't tell you not to bother. You gotta start somewhere. But offline is very different from online, and #r is very different from AC.