OT mechanics, help me diagnose this problem

Got plenty of oil. In fact maybe too much, which is my other idea. It's above the top line.

Clean the throttle body. Idle quality goes to crap between 75-90K in the 5.3l with no malfunction codes. Get you a can of throttle body cleaner and a 10mm socket to remove the throttle body. Using the cleaner and your wife/girlfriend/room mate's toothbrush clean all carbon build up from throttle plate. I also place a rag in throttle opening so I don't accidentally drop something into the intake. Then I clean the inside of the intake runner with the same rag before replacing the throttle body.

Good luck.

Yeah, they allegedly checked all the fluids. It was the dealer, which was my first mistake. I had been using a local garage, but his mechanic quit on him and I needed it done ASAP.

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Check the plug wires, they may have knocked one off

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This, or cracked a plug.

Vacuum leak. Start by listening under hood while engine is idling would be my suggestion.

You didn't mention a check engine light being on in the OP, so I assume it isn't. Broke wire/spark plug would trigger a misfire code and illuminate the check engine light.

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Nope, no lights, all gauges are normal, Sounds ok at idle, only rough under load at low speeds.

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Throttle body as has been said, possibly the mass airflow sensor(would throw a code normally), throttle position sensor, crank sensor, cam sensor normally all these throw codes but I've seen them go bad without lighting up the check engine light as well.

I would investigate the area where the mechanic worked changing your oil sensor. Chances are he/she bumped and disconnected/broke something.

Actually, according to the invoice they also replaced the valve cover gaskets, so I'll bet there's a vaccum leak there. Guess I'll have to take it back and get them to redo it.