Originally Posted by Trakhak

OP said "Hello, I’m hoping to find some help with a bike front derailleur function issue. I’m working on my brother’s bike (Trek 1220 Road Bike). Just doing some general maintenance. Bike has a triple front derailleur. I completed making sure the rear derailleur was tuned well and moved onto the front. I noticed the front derailleur cable was slightly frayed at the end and decided to replace it."

You're right that it's best to eliminate major problems before getting down to fine tuning. But if the only reason for replacing the cable was that it was frayed, that likely means that the shifting was fine beforehand.

My guess (assuming the limit screw hasn't been moved) is that the inner wire is now insufficiently taut to keep the chain on the big chainring. It's easy to get the tension wrong when installing a new shifter wire, especially with a road triple crankset.