Weird. The stock brakes on both the '95 Caprice and '96 Impala SS sitting in my driveway can hold the car in place. That was true when the engine was stock, and is still true after adding a shift kit, PCM tune, cat-back, intake, and valve train upgrades. It's been true on both the factory tires and the substantially wider aftermarket tires. It might be time for you to replace your brake material; you're seemingly endangering the other cars on the road.
When you're trying to power brake, BTW, you'll want to let up on the brakes just a little, and mash the gas. Don't ease in to it.