[Jack]

At least some roost trees are used year after year. I know of one roost tree that's been used for more than 20 years (not the same turkey, I'm sure). Just like with deer hunting, areas that have some attraction will draw game year after year- a good food source, a good strutting area, a good roost tree, etc.
By the 3rd week of the season, the birds will have felt some hunting pressure, I would expect (I don't know your specific area), so I would try to be as non invasive as possible - lots of listening for gobbling, and not much use of a locator call. Chances are, the gobblers have heard any call you can find, by the 3rd week of the season.
Look for open areas where a gobbler would strut- a cut corn field, a dirt road, open woods without a lot of underbrush. Finding a roosting area near one of those open areas would be a good start.
The classic (and easy) way to find gobblers if there are roads through your area, is to go out the last hour of daylight, park, and listen. Gobblers often gobble at dusk to get hens to roost nearby. If you can locate a gobblers roost, return before dawn and set up a few hundred yards away, near a spot the gobbler can strut. Often you can call him down off his roost.