In fact, just for hell of it, and because I am curious now, let's look at each of those five seasons in regards to yards per touch and scores:
2009 Chris Johnson - 2,509 yards from scrimmage on 408 touches = 6.15 yards per touch, with 16 touchdowns
1999 Marshall Faulk - 2,429 yards from scrimmage on 340 touches = 7.15 yards per touch, with 12 touchdowns
2005 Tiki Barber - 2,390 yards from scrimmage on 411 touches = 5.82 yards per touch, with 11 touchdowns
2003 L. Tomlinson - 2,370 yards from scrimmage on 413 touches = 5.74 yards per touch, with 17 touchdowns
1973 O.J. Simpson - 2,073 yards from scrimmage on 338 touches = 6.13 yards per touch, with 12 touchdowns
Interestingly, his 2,000-yard season probably wasn't his best season:
1975 O.J. Simpson - 2,242 yards from scrimmage on 357 touches = 6.28 yards per touch, with 23 touchdowns
So really, while Faulk in '99 bested his yards per touch by a lot, Simpson scored almost twice as many touchdowns, so you could almost argue that Simpson's 1975 season was the best season a RB ever had.