It runs roughly but still runs for as long as my foot is on the pedal so 900 rpm’s and onward. I replaced all my vacuum lines and made sure they were tight. Would a vacuum leak cause a truck to shut off as soon as I take my foot of the gas?It is still possible that you have a vacuum leak. Just because you can get it to fire and run for a few seconds does not mean there is not a vacuum leak. The fact that you can not keep it running at idle but it will run for a short time above idle is a perfect example of a possible vacuum leak. If the engine will not start and idle you cannot say that there is not a vacuum leak.