I have a 2004 Gt idrive 3.0. I think this thing rocks. It climbs well and everything.
Mtbr.com has reviews and everyone loves the version you mentioned.
But i think you will be happy with either bike. I cant comment specifically on the trek.
07 Fisher Paragon, 00' Lemond Buenos Aries, Specialized Langster, Schwinn World Sport SS townie, 99 SS-Works single speed conversion, early 90s Raleigh roadie rain bike, 07 Fisher Rig, Trek 520, and a home-modified chopper
I would guess that now Trek makes a better frame than GT. I haven't ridden either, but I would recommend Trek just because I think it's a better company.
Transition Dirtbag, Kona Roast 2002 and specialized BMX
If you are weight weenie the gtidrive is heavier.
I don't like the fuel is still pretty light and efficient.
The fuel has very poor suspension activity while pedalling and braking while the gt would be smoother (in theory and from what my buddy tells me haha) as the suspension should remain active while pedalling (no affect from braking, still crap)
Depends what you want really. Personally, for xc ,I might prefer the trek...this is a 55 to 45% deal. Both would be pretty equal for me.