At work one of our fleet trucks is a 99 with about 175k on it. It started running rough almost like a miss fire around 1800-2000 rpm. It runs good under and over this range although the power lately has dropped off according to the guy who drives it. We changed the fuel filter, then put on a fuel pressure gauge and found the lp only making 6 psi at idle. We put a new lp on and no change. The "water in fuel" light keeps coming on so we started filling at another truck stop and no change. We also started pouring in quite a bit of power service and no change. I'm not a 24 valve person, so I'm at wits end. Any other suggestions?