Eh, going on the line if one doesn't know what it is, then start eliminating the things it's not - timing being one question. One of those "it shouldn't" but at this point maybe worth verifying to cross off the list of possibilities.

*EDIT* - as far as jumping time, such as the timing chain taking a leap, my experience is that the motor will sound a bit uneven or outright loping rolling over.

Perhaps investigate whether enough fuel is being delivered as well as enough air - maybe feather the throttle a bit on the stretch that the IAC (Idle air control) is stuck shut or similar.

 

Agree with above posts to double check the timing
I'd start with rough timing the engine once more
Then, while the number one plug is out, you can check it for fouling
If the plugs are all wet, it will just want to start but not actually start
So, try a flood clear start after a rough time once again
*When up on 1 on the compression stroke, you can turn the key on and rotate the distributor and make it spark
When the #1 plug fires, that is the timing set
Make it spark at 10 degrees with the spout out (set the crank at 10 BTDC, rotate the distributor with the key on, when it sparks, lock it down)
Take note of where the factory chisel mark is at the base of your distributor
It will line up when the truck is at 10 degrees (unless something bad happened)