"Many may say be grateful, which I am"

"Many may say be grateful, which I am". My truck ran fine yesterday morning, later that day I went to go leave, I hoped in my truck it would turn over, but no start I tried this for five minutes the gave up skip to today I called the towing company to tow it to a shop well he took my keys and he started the truck up, I still took it over there mechanic said it was getting compression, he don't what the problem could be. Things I had done to truck? Ignition module, coil, wires to spark plug, spark plug, egr valve, catalyst converter, PVC, fuel fitter, battery, so why would it run that morning then, later that day it would turn over but not start. PS the truck runs now I'm puzzle has to why it happen.