Trolley Wearing Out

I'm looking for some help troubleshooting why the trolley of my garage door keeps wearing out. When my garage door is opening the trolley is tilting forward instead of running flat across the mid bar. Because the trolley is tilting forward it is digging into the mid bar and causing the trolley to wear down to paper thin metal and is grinding off the black paint/powder coating of the mid bar. I actually first noticed the issue because a black line of powder/grease started forming on the center of my garage door. I replaced the trolley and the replacement is now worn right out after less than a year. Could anyone offer some advice as to why it would be tilting forward instead of running flat and smooth across the mid bar? Any help would be greatly appreciated!