Blu Ray Choppy Playback

[bulgarianfreak55]

Specs:
M2N-SLI motherboard
AMD Athlon X2 6000+ 3.0GHz - not overclocked
EVGA 9800GT, 1 GIG
Creative SB0570 Audio Card
2 GB 800Mhz RAM
GGC-H20L LG Blu Ray drive (bought a pioneer and sony players to check if I had a bad LG drive and they played back laggy as well so I returned them )
Vista 32bit SP2

I am getting choppy play back in Power DVD9 Ultra. I downloaded TotalMedia Theatre 3 trial and its a bit better but still choppy and unwatchable (is there a difference between trial and full version?). Firmware and Power DVD both updated. Windows updated to most recent updates. Updated to most recent drivers of Nvidia the other day, hardware acceleration is checked. Processor is at about 10-20 percent usage sometimes a bit higher while playing Blu Ray, RAM usage is around 50 percent. One thing to note, the BD Dark Knight plays flawlessly...very weird. It is the only BD that plays perfectly. Any ideas? What things do you guys have installed and have good playback in terms of software, codecs, drivers? I had the CCCP codecs installed and removed them thinking they were confusing the player but it didn't help. Whats so special about Dark Knight that it plays fine?

Thanks guuys