You'll want to answer the question about fuel. Premium is the only thing you want to run.
Then the plugs and wires are next on the list of usual suspects. If you don't know when they were changed, it's time to do both the wires and plugs at the same time.
Most ignition issues will show up once the car is in high gear.
I don't see anything that sounds trans related from your brief description. If a trans was causing this issue it would have very few miles left in it.