the stocker is a 2554r, thats as much as I know...I'm not sure what trims in came in specifically, but yea bob is right the upper rpms for such a small turbo at 10psi or more really kick out a lot of heat and put it way past it's efficiency range....that's probably part of the reason why these turbos fail a lot
I had the stocker, the gt2860r (NOT the disco potato, the smaller version), and the .42 trim t3/t4 (thanks to bob)....out of all of them the stocker sucked, the 28 didn't feel much different but it gave noticeable horsepower gains (I probably didn't feel the difference cause I had a lot of downtime between turbos)...and the t3/t4 was amazing...quick spool, good power, and felt great while driving
alas, I'm going to bigger and better things with the build though...gt3076r is in it's future, once I get my beater track car and pick the project up again