2001 Dodge Ram engine performance

The first thing I would check is the exhaust system, because if it is stopped up it will run well at the initial startup but will start to act up after a short period of time due to too much backpressure. The way to check this is to start the vehicle and hold the revs at about three thousand and if you dont get a good steady flow of exhaust through the tailpipe you need to have your converters replaced and probably your o2 sensors.