What are some of the differences in between the 03-04.5 and the 04.5 to 05?

 

03-04 is the 305-555 engine. the 04.5-05 is the 325-600 engine it has an added injection event, different injectors and an electronic wastegate control on the turbo.

 

what does that mean for the average guy?

What year did the cummins get noticeably quieter? I drove some 2nd gen's and then 2007's only... I would like to look for the more 'modern' engine?... I heard that the 03 HO came with the 6spd, where the non HO came with the 5 sped? Is that true?

 

The HO in 03 got the 6 speed because the auto was not rated for the boost in HP and TQ. I don't believe there was a 5 speed in 03. The new 48RE tranny was mated to the HO in 04 and the HP/TQ went up to 325/600 vs the 305/555 in 03 for HO's.

The 3rd gens are the quiet ones, 2003 and up (5.9's).

Cya

 

Here is a break down of the motors and trannys based on year:

2003 S.O. Federal Emissions: 250HP/460lb.ft. Available with NV4500 or 47RE
2003 S.O. Calif. Emissions: 235HP/460lb.ft. Available with NV4500 or 47RE
2003 H.O. Federal Emissions: 305HP/555lb.ft. Only available with NV5600
2003.5 The 47RE was replaced by the 48RE automatic transmission and available with the H.O.

2004 S.O. Calif. Emissions: 235HP/460lb.ft. Available with NV4500 or 48RE
2004 H.O. Federal Emissions: 305HP/555lb.ft. Available with either NV5600 or 48RE

2004.5 (50 state legal) 325HP/600lb.ft. Available with either the 48RE or NV5600

2005 (50 state legal) 325HP/610lb.ft. Available with either the 48RE or NV5600

2005.5 The NV5600 replaced with the G56 6spd manual gearbox.
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In addition to Rob Cs list, the '03 and '04 have no catalytic converter, no third injection event (for emissions) and get better fuel mileage.

All third gens are quiet.

John