My car overall sounds louder. It's most noticeable at about 60 mph. Accelerates just fine, just overall louder. Engine light came on, code P0014 appeared.

so the service manual covers all DTC errors , read that yet?
no engine told or what transmission is there or POST VIN and we tell you what's under the hood. there are 7 engines used
the VIN code 8th digit is engine code as are RPO list engine code


P0014 (SM says) 6 engines do it, VVT errors. and 8 degree error was found,

Exhaust Camshaft Position System Performance

I would check the timing!
Definition of check engine code P0014:
Generic (Common for all car manufacturers):
"B" Camshaft Position - Timing Over-Advanced or System Performance Bank 1

could be a engine mount, any engine setting out of line will add more load to the engine mount movement, air leak in manifold, bad spark. it could als be something as simple as a thrown wheel balance or the balance on drive shaft balancer is out of sync, or missing.

Noises are decieving. Cud be steering system or wheels or suspension. If ball joint fails car cud flip ovr.hav pro testdrive it. Seek a gudguy at surecritic.com

Better check your codes again sounds like your converter is plugged up

The code P0014 is for Camshaft Positon Sensor Actuator Bank 1. The possible causes are incorrect camshaft timing, wiring problems (harness/wiring) in intake timing control valve solenoid system; continuous oil flows to VCT piston chamber or failed timing valve control solenoid(stuck open).
The code P0015 is for Camshaft Position -Timing Over-******** (Bank 1). Your problem will probably be that the timing will be slightly out, due to wear (stretch) of the timing chain; this will all be linked to the overall cold start issue and the timing position. Get that timing checked, or push for the full fix for the cold start timing issue.

What speed are you going when it chugs?
It could be as simple as a bad spark plug or a spark plug wire/boot grounding out.
When spark plug boots get old, the rubber cracks and lets voltage arc out the side and to the engine instead of through the plug.
This will be most noticeable when trying to maintain a speed of over 40 mph, or under mild acceleration.
The reason for being noticeable at this speed/acceleration level is that the transmission torque converter will be locked, transferring the vibration from any engine miss straight through to the wheels.

Did you reset the ECU after changing the sensor? If not you need to (procedure in 2nd pic below), that way the fuel trims are reset and the ECU can re-learn the Short term and Long term fuel trims. this could be the cause of the difference in MPGs.

An O2 sensor will have no effect on RPMs/MPH. the only thing i can think of that would effect this besides changing gear ratios, would be changing the overall diameter of your tires or possibly a slipping clutch.

Check the codes on the ECU. here is the procedure:

(CLICK PICTURES FOR FULL SIZE)

This could be a transmission issue or a catalytic converter issue hard to say with the limited info provided