Take it to Autozone and have them pull your codes for free. Come back with the results. The best way to diagnose these newer computer systems is to read what it's trying to tell you. And mostly the codes won't point to a specific sensor in general, but that it sees something out of range that might be caused by an entirely different part of the sytem. And as stated, if the engine hasn't been tuned up (plugs/wire), do so now to elimnate that as a possibility. But I only reccomend OE plugs, 3.0Ls are funny about what plugs you use.
1987 Ford Ranger Short Bed 5.0L/T-5 Project
1988 Ford Ranger Long Bed Parts Truck
1993 Ford Tempo 2.3L OHV HSC Auto - D/D Stock.
1999 Honda Accord VTEC Auto
2002 Dodge Caravan - 3.3L Auto