I installed a magnaflow exhaust on a 2005 tahoe with the 5.3. I do fell more power but when I drive it sensibly it seems like I have lost MPG. Does any one if this is normal?

 

I'm not an expert on mpg, but i do know that it should help mpg. The only problem i had when i installed my magnaflow on my silverado was that I drove at higher rpms so that i could hear the mean sound of my new exhaust and flooring it occasionally didn't help either. So, have you been hot roading it? If so, that could be your problem.