Avalanche/Chevy Trucks - 4 speed vs 6 speed

Anyone have any insight on the differences (gas milage, towing capability, performance) between the 2007 and 2009 Chevy Trucks? I believe in 2009 they went to a 6 speed transmission, where as the 2007 still has the 4 speed. I'm considering upgranding my 2004 Avalanche to a newer year, but am not sure if it's worth spending an additional 7k or so and getting a 2009 in order to get the 6 speed?

Also, are there any gear ratios to specifically go for?

Lastly, does the Z71 do a little bit better for towing? I think the suspension is stiffer on the Z71s?


Right now I have a 2000 XStar and the Avalanche does just fine towing it, but this weekend we'll be picking up a 2011 SAN 230. If my 2004 does okay towing it, I think I would like to stick with another Avalanche (just a newer one), but if it struggles I may consider getting a 3/4 ton diesel, or getting an Avalanche with a 6 liter.

Thanks for you input!