are two primary causes.
1. Either your battery is going bad, and the variable voltage a bad battery produces is known to produce this type of problem, or
2. The Electronic Control Module (ECM) circuit board in your dash has cracked solder (usually on the ground connection) and either needs re-soldered or replaced.
there's an entire thread on this problem at the dodge forums. Around page 3 or 4 the people who are posting on it start to identify what's going on and what exactly needs to be checked and replaced/fixed.
http://www.dodgetalk.com/forums/showthread.php?t=108869&pp=20&page=4