AND ...
Paralleling three LM317's is not the best way to achieve a higher output current capability. Better is to add a PNP power transistor around a single 317 (circuit is in the datasheet). If you want to stay within the 3-terminal-regulator space, best is to change to an LM350 (3 A) or LM338 (5 A) and get it all done in one device. Both of these methods have a single output voltage adjustment point, no tracking issues, etc.
A possible advantage to the external power transistor method is that is lets you control the relative power dissipation in the 317 and the transistor. This can reduce heatsink size or complexity, and both devices will run cooler than either a 350 or 338 for the same input voltage / output current conditions.
ak