I could be wrong but i think this is a general issue with the Gtab 10.1 devices. I have the WiFi version and watching transformers 2 on it is ok but when i play some HD stuff i have recorded it stutters as well.
Playing youtube in HD is a joke on the device.
I am hopefull that ICS will fix the issue. If not its going up for sale and ill try my luck with a Tab 2.
I ran into the problem when trying to play my own 720p videos.
I got BS Player and Dice Player. Both have plugins that take advantage of the Tegra hardware. I think the default player only runs off the CPU (can anyone confirm/disprove this?)
With those 2 players, it's still hit or miss on which codec is supported by the hardware. My 1080p videos are quiet stuttery but mostly watchable if there isn't a lot of motion on the screen. I get slightly better frame rates if I watch the video off a network share instead of off the internal drive. I use ES File Explorer to access the network share on my PC. I've never done straight benchmarking to but numbers behind all of this, it's just what I've noticed.