bzdqkq,
I have a 2009 Anniversary Edition 3400 RL that I drag around with a 2007 3500 SRW Silverado. I had the same problem.
The hitch was as low in the TV as it would go and besides I wanted to keep space between the TV and the Montana where it was so they wouldn't bump into each other. My solution was to add a 1.25 inch structural tube inserted between the axle and the springs to raise the Montana (I noticed the other day that Dexter has a raising kit) and I installed a set of Belltech lowering shackles on the TV.
http://www.streetbeatcustoms.com/200...ckles-Hangers/
I got mine from Lordco.
This has just about levelled things out, nothwithstanding the further air-bag complication explained near the end of this post.
The distance between the new shackle hanger and the spring is 7.25 inches, centre to centre (Canadian spelling) on the hanger bolts. I'm not at home and I don't remember the distance on the OEM hangers so you will need to measure yours to get the distance. Remember, because the axle is about half the distance from the hanger, you actually only lower the truck by half the increase in distance between the bolt holes on the new and the old hangers.
For the install, I found a good website, but I have misplaced the web address (at home again), suggesting you put a 4 x 6 piece of wood under the spare to lift the truck whenyou do the install. Worked great. I'll try and fine it later, if you want.
I have a set of PacBrake air bags on the TV that, prior to lowering, I ran at fairly high pressure because that pressure worked best for me (between 60 and 90 psi, depending on my mood). I needed to make sure that I didn't lower the TV so much that I didn't leave enough room for the deflated air bags. It seems to be working OK. At least the bags still hold air. I found that if I used the former higher pressures, I was carrying all the weight on the air bags. This resulted in a bouncy ride. I now run them at about 30 psi and all is well.
One last caveat. If you aren't using air bags (which raised my loaded TV about 1.75 inches), you may only need to do one of the things I did to level out the Montana.
I hope this helps. Good Luck.
Rob