Not ruling out some of the other potential problem areas mentioned here, I have brand new struts from Houston and on a cool day like today (54 degrees) even when I help it up, it still sags back down a couple inches. Definitely wait until warmer weather before messing with the torsion bars. You could cause more problems down the road - like a bent door (taco-ing) or causing the roof box to come loose.
If you do find that it's the torsion bars then get some help with them. You can do serious damage (expensive) if you don't know what you're doing.
Cheers
Steven