The 08 is much better than the 07.5's. Many of the bugs have been worked out. As far as performance, my 05 with an Edge EZ, AFE CAI and straight pipe for the cat and muffler ran a best of 15.16 with 50K on it. My 08 with just an AFE Stage 2 with Proguard7 ran a 15.21 when it only had 2K on it. The 6.7 will run circles around the 5.9 and when it comes to pulling you can't even come close to comparing them. I owned 7 5.9 CTD's and wouldn't trade my 6.7 for any of them.
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2008 Ram 3500 CTD 6.7/68RE/3:73 LSD (It was built right, nothing fell off)
Previous Rams: 1990 CC Dually, 1994 RC LB, 1995 CC SB, 1998 QC Dually,
2000 QC Dually, 2001 QC Off Road, 2003 QC Dually, 2005 QC Dually
REAL TRUCKS DON'T HAVE SPARK PLUGS