Car tends to die sometimes when you take your foot off the g

1999 Dodge Durango
5.2L V8 with 146000 miles

the car has days where it dosn't start very easy and when it does start when you take your foot off the gas it dies. When you drive as long as you don't stop or when you do you keep the gas pedal pressed in some to keep the rpms up. Any help with this would be great.

Thanks,
Nathan Leochner