Per Ford about 100,000 miles. Search for changing info. The 05 to 08 have a two piece design that can break. There have been several threads addressing it, they can be safely changed without breaking. If you have two piece, it might be a good idea to change them now.
chevy runs deep, Don't step in chevy!
289 - Holley 4150 570cfm; Performer intake; mild cam; MSD HEI; 302 heads; Roller Tips; Hedman Tri-Y headers; H-pipe w/Flowmaster 40's; 9 in posi 3.50; 205/50-17F; 225/50-17R.