Over torqueing them with an air gun.
It could be a stuffed catalytic converter.
Sometimes when you run a vehicle out of fuel trash in the bottom of the fuel tank can get picked up and clog the filter try changing your fuel filter and see if it will start.
timing chain has too much slop and rubs side of timing case
It isprobably not getting fuel or not getting spark.
A vacuum leak is one possibility.
check igntion coils
There are three relays in the fuse box. One of them is sticking. Replace all three, they are $11 each.
The starter is burning.
the Bering is going out or something got in the housing
Check the temp sensor on the thermostat goose neck. Mine got broken and when the truck warmed up it wouldn't start. Let it get cold and it would. about $25 at a parts store.
Clogged fuel filter, or failing fuel pump.