2006 GMC Sierra HD Diesel vrs Ford F350 Diesel..Help

Hi All, new to the forum and I have a question for those who know the 06 diesel trucks.  I am looking to buy the following:

2006 GMC Sierra 2500HD Diesel crew cab 4x4 S/B (has 75,000 miles on it) but is in excellent shape and has the coveted "Better" engine (Has a D in the serial #) (apparently they made 2 engines that year, this one has the preferred one)

My questions are:
How will this pull my 12,000lb 5th wheel?
Do the 16inch rims/tires pose a problem?
Any major issues with the 06 truck I should be aware of?

I hate to say this but the other choice I am looking at is a 2007 F350 Diesel Lariat Edition w/35,000 miles(sorry) anyway, price for the GMC is $6,000 CDN dollars lower than the Ford (due to Km and year). I like the quiet of the GMC, but like the beefier size of the ford. Ford seems to be roomier inside also.  The truck will be a pleasure truck (non work), and used for trailer towing

Any comments/thoughts/suggestions appreciated

Thanks  

If you're talking about the LBZ Duramax, then yes, that's the one to get. That's a great motor that's quiet and has lots of power. Shouldn't have any trouble pulling 12,000 lbs. GMs generally have the smoothest ride, too.

Generally, the Ford has a beefier chassis, but they have had more problems with the engine. '07s should be OK, but the 6.0 doesn't have the greatest track record.

Either way you should be OK.