I have a 99 DOHC, 55K miles. Last Saturday, I drove about 45 minutes at a pretty steady 50-60 mph with the a/c on. Car ran great for the first 40 minutes or so, but suddenly going over the crest of a small rise in the road I felt the car shudder just a little, as if it were going to stall. I took my foot off the gas, and noticed it was idling around 1200 rpm, way lower than normal for 50 mph. i pressed the accelerator, and the rpm dropped to 600 rpm and the car really started bucking. as soon as i let my foot off the gas it went back up a little, maybe 800-1000 rpm, and just coasted, hesitating a little every now and then. I pulled over at the bottom of a small hill as I knew I wouldn't make it up the next slightly larger rise in this condition, put it in park and it idled very rough. Turned off the ac, no change, turned off the car, waited a minute, started it back up, everything golden, 5 miles down the road, going down a long gradual hill, felt it shudder again and no power again, put it in Neutral, shut it off, restarted and was fine again. This was happening with a little less than 1/4 tank of gas. Since I was meeting someone at a gas station, I filled the car while I was there, and drove the entire distance home with no problems at all. Have driven so far this week with no issues. Could this be a weak fuel pump?