Sold my 97 12v and got the 08 in Oct. LOVE IT!! Auto is great, good solid shifts and with 2 OD gears running 1800 RPM at 70. Trans shifts and overall performance is very close to the DTT in the 97. Love the quiet and just enough noise under accel to sound good. The Ex brake will make tailgaters eyes get real big, especially in Tow-Haul. First time I tried it I almost ate the windshield as it downshifted.
Find taking trips less tiring than in the 12v. Steering and brakes are much improved. The little bit of wander and the noise of the 12v was tiring on long trips. Been tracking fuel economy and on a trip to So. Cal averaged 18+ hand calc. Used cruise most of the time and maintained 70. My mileage locally is 14. 5 but I tend to have a heavier foot than when in the 97. Just to much fun to keep my foot out of it. Overhead so far has only been a couple of tenths off of calc fuel mileage.
When I drive for economy I get almost the same mileage as the 97, had 4. 10s in it, but just can't do it all the time. This truck is to much fun to drive so I don't drive easy very much. Both trucks were in the 17 MPG range in local, normal driving.
No codes yet. My main concern is the quality of fuel. I pay a little more to get fuel at stations that sell large quantities and make sure the pump is labeled ULSD, except in Calif since that's all they can have. As time goes by the transition to ULSD should have purged all the old fuels from stations.
As far as the smog crap, I think the learning curve is going to be steep and fast since most of the Engine control stratagies for good running emission engines have been developed over time for gassers. . Don't like it, but we have to live with emisson control. The EGR on my 97 came on at 140* ECT and stayed on except for WOT (until I took it off). Newer EGR systems constantly vary it depending on conditions engine is being used. Right now I have no plans to mod performance, but that will change as the warranty runs out if like other vehicles I have owned. There is no such thing as to much power!!
Love the new truck!!