Personally I put Lara's 2003, 500+ run series performance against Aus (533 runs in a 4 match series) on par with his much more famous 99 series performance against the same Aus team.
While the 1999 series was almost like a God-scripted "Rise from the Ashes" story from Lara's perspective, I felt he was not 100% fit, still struggling with the persistent hamstring injury. He gave way too many chances while batting (too many for my liking).
It was more of a phenomenal mind-over-matter performance from Lara in 1999, he pretty much collapsed in the ODI series that followed immediately.
In 2003 series, I felt Lara batted with tighter technique. He looked fitter, gave fewer chances, even when he took the Aussie fast bowlers head-on.
Brett Lee really threw the kitchen sink at Lara in that series, but Lara answered fire with fire. Their battles were magnificent to watch, with both having their moments of superiority.
It started on the very first day of the Test series itself, from Lee's first delivery to Lara, and with the first runs that Lara scored in the series - a magnificent, aggressive square cut boundary off a 92 mph Lee missile.
I still remember in the last Test in Antigua, it was a green wicket, Aus were bowled out for just 240 in their first innings, and in the West Indies first innings, when Lara walked into bat, Steve Waugh set the field just for fast, short-pitched bowling.
Brett Lee charged in, coming around the wicket, and Lara square cut the very first delivery he faced over point for a 6.
You just don't see that often in Test match cricket, a great batsman hitting an express fast bowler for a 6 on the first delivery he faces.
It was incredible theater.
Starting from that 2003 Aus series, till the end of his career, Lara finally worked on his fitness, overcoming the long persisting hamstring injury that plagued him for several years before that, and for the final 4 years of his career, he quickly regained back the same remarkable consistency that he showed in the first 5 years of his Test career.