Q: I have a 91 cadillac deville with 90,000 miles. If i drive short distances it runs great...if i drive long distance (45 min +) esp

My 91 deville runs great driving short distances but when i drive longer (45 minutes+) it will begin to sputter and if i try to accelerate nothing happens. I usually pull over and shut off the engine. If I'm stopped at a light when this is happening then it will not accelerate and seems to want to shut off. It will restart fine and will drive but almost immediately will start sputtering again. This seems to happen on hot days and longer trips. Any ideas?

My car has 90000 miles.
My car has an automatic transmission.