and the RPM gauge read 0. But the truck ran fine
You have another issue going on there.
I noticed the temp. gauge is not always working. It will not read the temp. It did it the other day for about 3 miles. Then stopped
I'll bet you have a bad ground.
Since changing the PCM twice gave you a temporary fix, I would check the ground that goes to it. It is usually near the firewall.
Check your battery connections, the big fat ones, and the little ones to both sides of the radiator support, and the fenders, firewall, etc.
__________________
BroncoJoe19
2006 Alt Fuel Jeep (electric)
'98 windstar 3.8L
'99 Crown Vic 4.6L
'90 Full Size Bronco 5.0L
I'm not a professional mechanic, take my suggestions with a grain of salt, or a cup of coffee 
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