Thanks all for your input, suggestions and tips! Yes, sorry, the code was a 24, not a 26 (typo). I was measuring the O2 output with a digital multimeter, so I checked it this morning with an analog scope. Once it fully warmed up, I saw pretty choppy waveform on the screen, though it appeared to be fairly uniform, ranging from 0-1V. Also ran a min/max/avg test with my multimeter and it averaged at 0.69V, with 0.95V max and 0.43V min...not sure if that info really helps. The connector on the wire going to the O2 sensor appears to have gotten really hot at some point as the connector's insulation slides right off. Not sure if it's the original or not.
I inspected all the vacuum lines with my vacuum pump and they all hold 25 in Hg without leaking. Checked the two wiring connectors near the throttle body (large circular plug and flat 3-wire plug) and the terminals are clean and connections are tight. Insulation looks fine. I removed the firewall (on both sides of the ground strap..firewall and intake manifold) and engine block ground wires on driver's side rear of the block and polished each connector and their mating surface and covered them with dialectric grease. They all seem to have great continuity.
Checked ignition timing with the CTS disconnected and it jumps between 10 and 12 degrees, everytime it misfires. When I got the car, it had this same misfire, so I changed the usual ignition items like the plugs (Champion), wires (Bosch), cap and rotor, but that didn't seem to help. Speaking of the CTS, I noticed that I can rotate the plastic connector back and forth along with the two terminals...not sure if that's attributing to the problem. I did disconnect the O2 again this morning, once warmed up, but this time the engine started chugging at idle and running really rough...like the choke was on. Thought that was strange since it seemed to run better yesterday with it disconnected. I let it idle for a few minutes and it eventually stalled. Measured the resistance across the CTS and it was 1100 ohms. I reconnected the O2 sensor, started the engine and after a few minutes, the chugging stopped, but the miss returned.
I had thought that maybe there was a problem with the fuel injector, as I was seeing small droplets of fuel beading up on the throttle plate and running off, so I replaced it with a new Mopar (Bosch), part #C3940292. I don't see the droplets anymore, though I can still see fuel running on the throttle plate, but the misfiring symptom remained the same.
Not really sure what else to check at this point. Any ideas? Thanks for reading.