I think that 2.25 isn't too bad compared to what a lot of 6spd LS1 friends get on street tires on the same track. The 2.40-2.52 ones aren't great though. You are definately leaving some on the table. Driving around the water box next time and then just quickly scubbing them to get the debris off may be the way to go for next time out.
Check with a few other LS1 guys - see where they shit at. You might pick up some by revving it out a bit more. You said that your tranny doesn't shift properly - how many kms are on you car?
Also, what gears do you have?