2000 Other Jaguar Models engine cuts out

I have a 2000 jaguar S type with a v6. The car starts with no problem idles fine and runs great. I don't have any problems accelerating from a stop. The only time I have any trouble is at a cruising speed. If I hit a small hill and have to give it a little more gas to maintain speed it chugs and acts like it's cutting out. I can give it alot of throttle and it will stop chugging and accel fast with no problem. At first I thought it was my transmission or the lockup converter not working properly. The more it happens the more I think it's an engine problem. Any advice you could give would be great. Thanks