If you have a 3.5:1 you shouldnt have any problems leaving most cars behind at the lights. I think you probably have the 2.8:1. You can add a stall converter to bring your engine up into it's power band, however a stall converter combined with a tall diff ratio (such as the 2.8) is not particularly driver friendly. At speeds below 100, even when just accelerating lightly (ie from 70 to 80) the engine tends to rev up to the stall speed, which can become very tiresome, especially if you experience some exhaust drone.
I would recommend you check your diff ratio, and if it is a 2.8, go down the path of a ratio change (3.25 or 3.5), and then if still not happy, perhaps a mild stall converter.