All of those vehicles will work for your family and choice of 8000#(+-) TT.
For me, the risk of high repair costs on the 6.0 PSD would scare me away from that one.
What sold me on the 8.1L Suburban is the diesel like performance for towing and higher carrying capacity. The hitch swap to a class 5 was a 20 minute job. Didn't even remove the spare tire to do it.
My last big trip towing a 7200# 34ft TT(it was more at times if I had to carry more than 10gal water) was from Michigan to the Oregon coast and back with 3 adults and 4 kids under 12. Total passenger weight was 900#. My TT tongue weight was 1100# measured with a Shurline scale before leaving. The Burb handled the weight amazingly well. I even towed down the Teton Pass to get to GrandTetonNP and YellowstoneNP and without a doubt wouldn't want to have done it with a lesser vehicle.
If you go with a Ford diesel, make sure you have a good exhaust brake to slow down so as not to lose your brakes.