My truck will not start periodically when it sits for a couple of hours. By periodically I mean every 3rd time or so. I have tried injector cleaner with no change. Ether helps.
Since ether enables a start, then it’s a fuel issue. You don’t report any problem starting it cold. That’s an odd combo since I’d think it was some fuel pressure thing where the starting mode just can’t produce the squirting to manage the start, but once started, it can manage to allow it to run.
Have you done the key trick and counting the check engine light flashes? …where you do (DO NOT START) ON-OFF-ON-OFF-ON (leave ON) and count the flashes. It will form double digit codes. Short pause between first digit and second digit …longer pause then on to the next. Easy enough to figure since you know that they always form double digit codes. You can just write down the grouped flashes and form them up into paired sequences.
You will always get code 12 for some odd reason and, iirc, you will get 55 at the end. You will only get 55 if there are no codes.