1991 Chrysler Le Baron 91 labaron sputters and stalls after

This only seems to happen after it warms up.It started two years ago.It got worse over time to the point that it will just sputter u home.Then like yesterday when it cools down i can crank it and do donuts it my yard like a top nascar driver.The car has been sitting now for a 1 and ahalf.I crank it and drive every month are so.That was the first donuts.My mom drove the car 6 years and the only problem she had was the trans went out.It was under warranty with the dodge place.Because it was own by a older couple and it was in great shape.It still is with it plush red velvet seats.lol.I dont want to crush this car.I have replaced wires,plugs,cap,button,oxygen sensor,drop gas tank cleaned,replaced fuel filter.The first thing i thought was wrong thx to my uncle was take out the cat convert.It was replaced with a strait pipe.I don't know how smart that was,with all the sensors.That didn't help it.It was only doing it sometimes then.We where still driving it then there wasn't any change.I would love some good advice and be very greatfull for anyone's time in helping me.HAHAHA no wonder there not many reply's to answers in the forums.MONEY,what else could it be.