Two suggestions about improving this truck from personal experience.
1. The seats seem to be inadequate. For short trips they're fine, but sit in them for 2+ hours and they really demonstrate how they need more support. They just aren't big enough physically which seems to be the obvious problem but is excusable since the truck isn't very wide. I wonder if shrinking the Avalanche/Silverado seats would be possible as those are beautiful seats that are extremely comfortable.
2. The transmission although extremely smooth, seems to be geared far too high. Though this may get the truck good mileage, it isn't the best for those of us that want to accelerate quickly or pass. Under average acceleration from a stoplight, the current 3.5 in the crew cab with the 4speed auto is perfect. But tach out the shifts and you notice what's wrong. At redline in 1st gear, the truck has just hit 80 kmph (50 mph). This is an extremely fast first gear! Shifting into second is smooth but the rpm drop is just too much and the power drop is quite apparent. But, as the rpm's build , the truck starts to accelerate hard again right up to 120 kmph (75 mph). In conclusion, an extra cog in the tranny would pay dividends in the 1-2 shift and the 2-3 shift in the auto transmission. Although the new power is greatly welcomed, a 5-speed auto would just be the icing on the cake for an already great vehilce.
Overall thoughts: GM got this truck pretty much perfect in my opinion right from the get-go except for transmission and the seat quality/comfort. The 3.5 engine is beautiful (excellent mileage and power), the interior is logically laid out, looks good and is very funcitonal for various types of people (workers, average city driving person, the adventuresome person etc) and it just looks great overall. In my opinion this is the best midsize on the market, regardless of whether or not the competition has a bigger cab, more pulling capacity, or a V8 option. If you want those features, get a full size...that's why there are different classes of vehicles.