Just use the Motorcraft Fuel Filter...I've never heard of any other type of fuel filter improving mpgs or hp. It doesn't really make sense since the fuel pump does all the work...and for more fuel to be injected you need to adjust the ecu and have larger injectors.
I replaced mine at 58000 miles and it really wasn't that dirty...certainly not clogged. I would guess your 08 has fairly low miles, so it shouldn't need one for some time...my guess to have it done at a Ford dealership would be about $60-80 with labor and parts.
You could do it at home but prepare to get wet
12 Black GT500 SVT PP l 2.6 Pulley/Idler l Airaid l o/r X l 305 NT555R's l Recaros l
04 Azure Blue Mach 1 / 03 Sonic Blue 3.8 / 14 Sterling Grey F150 FX4 402A 5.0 / 11 GT500 R.I.P.