Pre '06 had known issues with the side mirror folding motors going out. This was fixed with the new '06 style mirrors. You can tell them by the front of the mirrors. The older ones were a large plain chromed cap over the whole front of the mirror. The newer ones just have a chromestrip across them with the H2 logo.
The interior changed in '08. It lost the "boobie" :cheers: hvac vents, as they are known, and became a flatter more modern design. I personally like the pre '08 interior better. It is totally unique to the H2. Post just looks like every other truck out there imo.
Adventure package has rear air bag suspension with on board compressor. It auto levels to compensate for loads, and you can manually raise the rear like 4" on trails. It is a decent system, and looks great on paper. In reality though, if you blow a bag on a trail, or anywhere, your rear end just squats all the way down and you have no suspension. Most people convert them to coil springs once they stay having issues, as it is way cheaper than repairing the air system. Also, if you plan on lifting it, I believe you have to dump the air system and go to springs anyway. The on board air compressor is cool, but is not really anything special. You can get better performing 12v compressors.
'05 I believe was the start of the third row seat, and it was only one seat. I think in '08 it went to a full width two person seat. I'm not 100% certain on those years though.
'03 6.0 was 316 hp, '05 bumped it up to I think 325. '08 brought the 6.2 and 6 speed transmission, and I think 393 hp. Sadly, we never got the 400+ 6.2 that the Cadillac Escalade got. [emoji26]
One thing to check for are broken exhaust manifold bolts. Usually the rear on the drivers side I believe.
That's a start. I'm sure there will be lots more info coming. You would love the H2! Only real issue is gas, and if you plan to do trails in the NW, learn to fit with less than 1/4" to spare! And I'm not exaggerating. Ask h3slate!