Ill be catching a flight from Tijuana to Mexico City. Can I travel with my US passport or will I need to get a Mexican passport?
You can't get a Mexican passport unless you are Mexican citizen.
Generally speaking, for travel you need a government issued identification document with your photo - a passport any passport qualifies for this.
Depending on the flight, you may also provide other forms of identification in lieu of the passport (for example, a driver's license is accepted on most domestic flights in the US - even from non-citizens).
In fact, depending on the circumstances - the document doesn't even need to be valid/current (for example, if you are trying to prove your right to enter by citizenship, an expired passport will suffice).