If it is an LS2 from a TBSS then it is actually a 4L70E trans. Samething as a 60E but better internals from the factory.
The LS2's make an honest 400hp/400ftlbs. My wife has a 2007 AWD version and is a low 14 second/high 13 second truck at 4,900lbs, tows my truck with trailer with out any problems. Her AWD version get's 16mpg mixed driving, freeway it get's high 19's. I would assume in stock format that it would get low 20's if just 2wd.
Go look at the casting numbers.
Head casting should be a 243, here is a link to it's location:
http://f.imagehost.org/0502/292.jpg
Block should be 12568950 and found on the back top drivers side.