Re: 07 F250 5.4 engine no power
First, are you telling us the dealer did not see these codes?
Second the 171 is ok but you got the second one wrong.
191 should be a 174.
Those two codes go togather for an air leak in the intake tract for both banks.
Look over and feel all the rubber fitting for being hard cracked or soft and letting air into the intake tract. Don't miss any.
This causes the fuel tables to shift out of limits, setting the codes and changing the engine fueling.
It's not the OX sensors or fuel filter doing this.
Cats could be restricted but clear the cause of the codes first.