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I just bought a 1998 Ram 1500 with the 5.2L motor. I was on the way home and set the cruise at 75 in overdrive. It slowly started losing speed and would hold the cruise speed. I took it off of cruise and I had to stay on it to keep my speed around 75. After that I took it out of over drive and the cruise held and with the cruise off I could hold speed with little pedal pressure. Now of course with overdrive off it sit about 3000 or so rpm’s at highway speeds so I’m getting terrible fuel mileage. Any help on this issue would be really appreciated as the truck is really nice and I don’t wanna feel like I was dealt a lemon in disguise.
 

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Needs a steady vacuum to hold the cruise control diaphragm. Bad/old vacuum lines or a leaky diaphragm will suck in air and release your settings. you can test the system with a handheld pump/guage to find vacuum pressure drops. Hoses run the heater, four wheel drive, cruise and a few other things. The worst vacuum leak you might have is,,,,,,, a manifold plenum leak. None of these I would consider terrible bad news, just things to check and maintain. Lots of reading to gain knowledge on this subject and youtube has endless video's on these trucks also. You should mention if it's four wheel drive, what's the mileage, big tires on it? and do you live in the mountains. 75 is the new 55 :cool:
 

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It slowly started losing speed and would hold the cruise speed
:confused: ??? Was it going faster than the cruise speed? Check the vac line going to the actuator under the battery. It fails a lot in the second gens. Also do you have the wild vent issue? There are check valves that keep vacuum in the reservoir that can fail. Usually one right off the plenum and another by the reservoir.
 
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