Timing by ear leaves ALOT of room for error. It's a good way of getting it going after a pump change, or temp fixing a drastically mistimed engine.
Even using the trick with the cold advance, still has like a 5* +/- and that's if you have a REALLY good ear.
PM Icanfixall, get in his timing meter rental program. The Kent Moore meters he uses are really easy and accurate to the tenth of a degree.
If your truck is running ok right now, and not sounding like a rattle trap, don't worry about the timing. Sure it will run better once you have it timed correctly, but you really can't do that without the proper tools.