I recently installed markmc's 3" suspension lift, panhard bar drop bracket, and wheel spacers. I also went to a 32" tire. I have 4WD, but don't (yet) have a G80 locker. All of that considered, the trip I did this weekend is pretty much the maximum of what I think we're (the Trailblazer and myself) capable of right now.
I started in Fairplay, Colorado and ended in Eagle, Colorado. First, I went over Mosquito Pass, which is a class 4 ranked trail that many claim to be the highest drivable pass in North America at 13,185 feet above sea level. I spun the tires a few times on some steep rocks and took a wrong turn at one point, but eventually figured it all out. This placed me in Leadville. I then went over the class 2 Hagerman Pass. After the long drive out into the Hunter/Frying Pan Valley, I headed north over the class 1 Crooked Creek Pass and found myself in Eagle.
I'm going to give some more details here, especially on Mosquito Pass. That's a pretty rough trail, and a few other SUVs were turning around and giving up before the hard sections even started.
Mosquito Pass
I went east to west along the pass, from Fairplay to Leadville. I'd recommend anyone with a similar setup to my rig do the same. Mainly, there is one specific spot (the first left turning switchback when descending from the pass) that presents a rock ledge that I highly doubt I'd be able to climb. (Sorry, I didn't get a photo of it.) If the weather were rainy, I probably wouldn't have been able to climb the east side of the pass.
Starting from Fairplay at the junction of Colorado Route 12 (all mileage is based from here), travel is relatively uneventful for the first 7 or so miles. At 7.1 miles, there is a sharp left and climbing begins. The rocks start here. A few stock SUVs were attempting this section and quickly gave up. This rocky section continues for a while until the trail turns west and reaches the mine at around 8.1 miles.
After the mine, the route is clearly visible for some time. There isn't much passing room here, and it gets steep and rocky. You definitely need 4WD at this point and having a diff locker will help a lot. I don't have one and I had to reverse and reattempt a few times due to spinning wheels.
After that long climbing section is done, you crest a shoulder and head a bit to the right. There is passing room here, but not for long. The trail becomes rough again as you climb to the summit. In late August, there were still a few snowfields close to the road here. The trail reaches the summit of the pass at 9.7 miles.
There are four roads, one in each direction, approaching the summit. Make sure you take the west exit. I went north by accident (it looked like the most used route) and quickly regretted it. On the descent from the summit, at around 10.6 miles, the first left turning switchback offers an interesting ledge. I doubt I'd be able to climb it. Getting down it was interesting enough.
The trail is relatively uneventful for the remainder of the trip, placing you in Leadville at around 16.4 miles.
Mosquito Pass tops out at 13,185 feet in elevation, and loss of horsepower at that elevation is really noticeable.