#1 thing for serious power loss on the contour V6 is stuck or inoperative secondary throttle blades, also known as the IMRC. It's easy enough to check if you know where to look besides the feel of it kicking-in in first gear.
Fuel filters cause power loss because of the pressure drop. Lower pressure on the injectors means less fuel per squirt, etc.

warmonger

Former owner of '99 CSVT - Silver #222/2760 356/334 wHP/TQ at 10psi on pump gas! See My Mods '05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red '06 Mazda5 Touring, 5spd,MTX, Black