2008-2009
Cleveland, 66-16, +8.9, 2 games, 2 games, 17-3.
Lakers, 65-17, +7.7, 2 games, 2 games, 17-3.
Boston, 62-20, +7.5, 4 games, 2 games, 18-2.
Orlando, 59-23, +6.7, 3 games, 2 games, 15-5.
2007-2008
Boston, 66-16, +10.3, 3 games, 2 games, 18-2.
Detroit, 59-23, +7.4, 3 games, 2 games, 14-6.
Lakers, 57-25, +7.3, 3 games, 3 games, 12-8.
New Orleans, 56-26, +5.3, 3 games, 3 games, 13-7.
San Antonio, 56-26, +4.8, 4 games, 3 games, 17-3.
I will go back as far as I can using ESPN's data, but so far, it looks like the longest losing streaks have been 4 games and three games.