I do really well under pressure, so I'm wondering what the highest stress jobs in aviation are?

Air Traffic Control. Often called the most stressful job in the world.

Another high stress is the Customer Services Agents at the gate - getting the passengers onboard and ensuring the aircraft departs on time. Flight Attendants have a high stress job of dealing with 150 + passengers from 1 to 12 hours or more at a time. You are everything for those passengers. 1st responder if there is an onboard medical emergency. Police Officer to handle any type of disagreements, Waitress, etc.

Being a pilot, whether at an airline or as an instructor, is a high pressure high stress job. There are many times at an airline, such as at altitude while cruising, that can be less stressful.
Takeoff, planning for and executing a descent, or an emergency require you to be on your A-game.
Flight instructing, especially brand new pilots, can be a high stress job as you are training someone with 0 experience how to fly. With brand new pilots, there is not time that you can let your focus slip.

There's was a time when air traffic controllers at Chicago o'hare dealing with take off and landing traffic were required to take break from duty station every thirty minutes at peak traffic hours because of high job stress because multiple runways crossing each other were being used simultaneously for departures and arrivals but with improved computerized traffic handling tools, dealing with this high stress situation may have eased. Those controllers were at that time highly paid employees until President Reagan fired the leaders of their employees union due to industrial action.

Similarly flying into or out of Heathrow London, Frankfurt, Chicago O'hare was highly stressful situation when the pilots have to pick up the ATC Fast Talking departure /arrival verbal clearances very proficiently and reading back those instructions correctly in few seconds because this ATC controller has to give instructions to the next traffic. Those controllers were extremely busy and were issuing instructions to flights continuously with out break. Timing was every thing.
As flight crew me,bears , pilots have to remain ahead of the aircraft with lot of forward thinking so that nothing comes to you as a surprise. Flying is a dynamic situation because your position is changing very fast and situational awareness not only about your own flight but about the traffic around is very critical. Although Captains are legally responsible about the safety of all the souls on board but flight crewmembers should not be distracted with small passenger management issues. Captain and copilot have to act as team because flying these airplanes is a team work and flight crew members have to be very disciplined

But my vote for the top stressful aerospace job will go to position of Astronaut because this job takes you to the next frontier for mankind. It is hard to imagine a more stressful job than traveling in space where very few have travelled so far and there is so much of beyond imagination challenge there.