Oh yes, you can mod the engine up to crazy levels. The problem is without knowing the weights we don't really know where the next shortcoming is. Are the rear tires overloaded? Are the axles overloaded? Is the suspension up to the task?
You already used the engine power to burn up some stuff in the trans. I'm not an internet policeman so I won't start with lectures about insurance policies, liability issues, and the moral implications of knowingly being over the ""G" numbers. A trans upgrade will likely solve the problem with the trans, and will lots cheaper than a new truck.
If the 2009 truck will do the job, can you sell yours, and buy a 2009? The difference in year and kM certainly shouldn't be nearly as painful as a new truck, even after your trans rebuild.
