You might want to read
this comparison test on the vehicles you are interested in. If you like your current truck, you'll love a 2007.5+ GM HD gasser. The 6-spd trans really makes a large difference in how it pulls plus all the other improvements with GMT900 over GMT800.
If looking outside of GM, I recommend Ford's 6.8L V10, skip the 5.4L. 2011 offered the 6.2L which is also great. The Ram I do not like the trans gear ratios compared to Ford/GM 6-spds. But the tests and owner experiences all say it is strong. If you go with gas, find a shorter axle ratio truck. 4.xx instead of 3.73.