Hello Again. Thank you for the additional information as this aids greatly in the diagnosing process.
First of all any battery that goes below 11.0 volts should be recharged or replaced. Seeing that yours drops into the 6 range during crank tells me that it is highly, highly probable that your battery is bad.
Before buying a battery I would highly recommend checking all your connections at the battery, starter and ground. If one of these are not on good or has some corrosion, it will cause havoc on your electrical, starting, and charging system.
If all connections are good, replace battery and then verify that your alternator is charging by connecting your meter to the battery while the truck is running. The meter should read 13.1 volts or more. If not you may also have a charging problem that is killing your battery.
All the problems that you described are a result of a battery that is going bad. The reason for the clicking is that the relays are operating incorrectly because they are not in the proper operating range. The starter does not have click as the battery does not have enough amperage even to turn the solenoid or starter motor.
If you have any doubt about the battery- bring it to a local auto store and ask them to do a load test on it. This will verify if the battery is bad.
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Edited by AdamsAuto on 7/2/2010 at 4:12 AM EST