The difference of night & day over my '99 3500 w/5. 9 . The '99 has been a great truck and with 215,000 mi. on it , it still has a lot of life left. The new '07 3500w/6. 7 is quiet, more responsive and roomier in the cab. The new truck is an SLT , so it is more comfortable too. The '99 has 5spd. w/ 4:10 rear and 16" tires. The new one has 6spd. manual w/3:73 rear and 17" tires. I was a little nevous about going to higher ratio & taller tires, but with the increased HP & VGT turbo the '07 will out perform the '99. All of my trucks are stock, as they'll do anything I ask of them. Hope this helps.
Jim
'99 3500 C&C
'05 2500 QC 4x4
'07 3500 C&C 4x4