Gta iv ps3 hdmi question?

May be...

on the back of the case it says it supports 720p, 1080i, and 1080p but i can only get 720 p how can i switch it to 1080i

Go to "Display Settings" and set it to 1080i yourself, make sure your TV is actually a 1080i!

First make sure your TV supports 1080i, go to display settings pick the one you want and you are allset. GOOD LUCK!!!!!