To do this you need a bike rigged with a bomb and rampage start Shakedown. after that make a replay over the save marker at Links view Apartment(you need to already own it). then go to the mall and shoot the first window, then park the bike next to the second window and wait for the rampage timer to run out. after that cancel the phone call and warp out of the mall and go to the pizza boy mission and right before you start the mission blow up the bike with the detonator.

I just found out how to do the sliding glitch. its really easy. all you have to do is to have a really short replay and then switch weapons to the chainsaw and at the exact same time play the replay. you can also take phonecalls and use weapons while sliding.