1999 Jeep Cherokee XJ 4x4 4.0L I6 180,346 miles AX4 transmission (Automatic)

I know about the search function but I was unsuccessful with it. If someone can provide a solid link about my problem I would appreciate it.

First off my CEL is on and the codes P0135 and P0137 are being presented. O2 sensor problem. Second when I start driving in second gear at about 1750 RPM's the propulsion stops and the RPM's go down for some reason. If I give it more gas, I hear a little pop somewhere in the front end then the drivability goes back to normal. I've been hearing like a ticking in the engine or drivetrain that I thought at first was a rod knock or equivalent.

Throw out some ideas, thoughts or advice. Or better yet, a link. Thanks everyone!