Last day or two I had been trying to figure out why I kept blowing #11 fuse on the JB when I drive a little bit. I tried everything everyone suggested. Ended up swapping the PCM. Has been ok since. What causes a PCM to go bad? Can they be repaired or just better tossing it?

 

They can be repaired. There are services that will do that for a fee. The fee varies quite a bit

There are a number of things that can cause it to go "bad". A wiring issue can cause a short and burn out a component. Internal solder joints can come loose after many years of vibration. Capacitors weaken and eventually leak causing an internal circuit to fail. PCMs are sealed units and the connectors are "waterproof". If any of the seals are compromised (due to age, heat, etc.) then water/moisture can get inside and wreck havoc.

 

Yup, what he said.

The transistors and capacitors don't last forever and sometimes solder joints crack.

​​​​​​Getting it rebuilt should get you down the road for another thirty years or so.