As for single season peaks;
Duncan 2002-03
Parker 2012-13
Ginobili 2004-05

Though after that, it's quite blurry for Ginobili and Parker because they were consistent but they also had to play through so many injuries.

For example I find Ginobili's 2005 postseason performance as an outlier because the surrounding seasons in 2004 and 2006 are not that good.

I think he was a better player in 2007-2011 time frame. But he was not fully healthy in 2008 against the Lakers. Then he missed nearly half of regular season then the playoffs in 2009. Then he was injured again in 2011, right at the near when regular season ended and it impacted the playoffs once again.

Parker's top 5 consecutive seasons are from 2009 to 2013 for me.

Duncan is way easier;
2001-03 top 3 consecutive seasons.
2001-05 top 5 consecutive seasons as extended peak.
1999-08 his 10 season prime.