I have been researching O2 sensors and most of what I read says they really only have a service life of about 80,000 miles. My truck has 4 O2 sensors and is at 108,000 miles. The MPG is suffering a little and I wonder if anyone here has changed their O2's out as a maintenance item (meaning there is no check engine light on) and if so did it help the MPG and performance at all? I have a 2001 Dodge Dakota with the 3.9 V6 and 5-speed manual transmission. I recently did a tune up with plugs, wires, cap and rotor and I use only name brand gas, Chevron or Shell. It gets a dose of Regane every 5,000 miles. My CEL is not on, I just wonder if new O2's will help. I'm interested in knowing how a new set of O2 sensors may help me and whether anyone else got any benefit from replacing theirs. I appreciate any info you guys can offer.