1990 Ford LTD lost power while going up a hill and now wont run

1990 Ford LTD mileage: 147,000. As you can see from the above information I have an "older" model car. I've had it a few months, but it hasn't been on the road until recently, reason being I was under age when I bought it, didn't have a driver's license until about a month ago. So all the time I have had it, it has only been started and run up and down our driveway. About three weeks ago I put it on the road, it did fine until about a week ago. My mother and I were started on a short trip to a nearby town and on the way up this stretch of hill, it tried to smother out and quit running. The day before I drove it up a secondary highway, very hilly terrain but had no trouble what so ever. Before we hit the hill, we traveled all flat highways without and problem ran like a top. After we finally made it to the top of the hill, we decided we would turn around and go back home. Again, it ran like a top. Now, it doesn't want to run much at all, it'll run a little way then die, start it up-it'll run a little way and die again. I do not feel that it is anything serious, but it sure aggravating, because I do not know where to start. I think it may be in the firing but I am not sure. It backfires sometimes. Automatic transmission if that matters. The car was a one owner, and my grandfather is acquainted with previous owner. I did not buy the car directly from him but from a local used car dealer in my area. My grandfather talked with the original owner about the condition of the car and was told it was in pretty good shape for the model. It has a great body for the model; it was a good buy considering I did not have a lot of money to spend. Thanks in advance, for any help you may be able to give me.