Updated/Edited

Got into my truck and started it up. Runs fine. Put it in reverse and it lost all power and shut off. Kind of felt like the emergency brake was on when I gave it gas to move backwards. Started it again, put it in reverse and same thing it just bogged down and turned off.

Interior lights come on but everything else is dead. Checked all my fuses. Fuse #20 (Audio, GEM Module, Powertrain control module(PCM) Transmission range sensor) was burnt out.

Replaced it and tried to start it. Just hear a click and thats all. Tried a few times, nothing. Fuse 20 I replaced did not burn out again.

Then relay 2 (Powertrain control module cluster) started clicking like crazy non stop even with the key out of it. Sometimes really fast clicking other times slower but rythmic.

At a loss I did go buy a new relay for (Powertrain control module cluster)

I put it in, turned the key forward and everything in the system turned on. Dash, fans, everything. I turned the key to start it and it went dead again. Now with the key forward nothing comes on. But with a new relay it did until I tried to start it.

I threw the battery in another vehicle and it works great. Newer battery so that can be ruled out.

 

From what you describe,
A good fully charged battery with power that has no place to go.
You want it to start, the engine wants the power to do that, but it just ain't happening. Why?

The power in the battery needs a good clean path for the power to get to the rest of the vehicle. What is in that path?
The connections at the battery, the condition of the cables to carry that power, the ending connections on the vehicle. One way to help isolate the problem, turn the headlamps on, attempt to start the vehicle . If the headlamps go out ,something is blocking the power from the battery reaching the starter. Either the cables are corroded or the connections where the cables connect to the vehicle could be the cause. Suppose we verify that is not the problem before going any further, can we do that?
r