I just had dual magna flow exhaust installed on my 05 f150 screw. Since having them installed, i am getting hard starts occasionally and recently have noticed when shifting from 1st to 2nd at high rpms when the truck shifts it backfires. The dealership told me they could find nothing and my exhaust guy told me it couldnt be the exhaust? What could the problem be? Not enough backpressure? Surely my truck isnt the only one that has ever done this?
HELP!

 

I have not messed with any catalytic converters everything is done behind factory stuff.