With stock tires, I'd be tempted to run the 3.31's. I'm not to familiar with the power of an LS but if they have the torque and power that everyone rants about, they might be just fine. You already have the 3.31 so why not give it a chance if your not planning on much towing. 3.73 will be good for power but at what cost to MPG. Stock tires to me would be no more than a 3.54 gear.
A 28in tire with 3.31 gears with a .70 OD will put you at about 2000rpm at 70mph
89 GW, 454, 700R4, 241C, 411's with posi's, 9" rearend, 2500 stall, lifted, and lots more to do.
1999 International 4700 Crew Cab 4X4, custom step side bed
2003 Durango 4x4
1982 CJ7 4 banger
2008 MB E320 Bluetec