I have a 2003 with 70k, the check engine light came and the two codes are p1170 and p0139. Truck just had new plugs, wires, and Maf sensor. The dealer said I need a new catalytic converter. Could it be just O2 sensors?

 

I would replace the O2's before I did the cats.
Replace both front O2's.

 

Based on those codes, you don't have a cat problem. Replace both the front 02's and then quit going to the dealer, who last time around sold you a MAF you most likely didn't need either.