[chuck's]

There should be two ground straps that are along the right frame rail just before the firewall.Are these straps in place and secure?It sounds to me that it is an electrical issue.I know you stated that the connections are good,but when things like you descibe occur this is where I go first.What about the computer connections?Clean and secure?The only other suggestion that I have is that within the wiring harnesses,some wires get crimped together and it could be possible one of these could be causing you problems.I refer to this because I worked on a 99 pick-up for two days with instrument cluster guages not working all the time ,only to find out that some wire from the cluster was not making a proper connection within a designated splice within the wiring harness.This is what the verdict was from the GM dealer.Since then there has been no problems with the guages.I hope this will be of some assistance and others will be able to help.
chuck's