Thank you for the straight forward answer, and the recommendation. When you upgrade to the 6.5 NA, do you also have to upgrade transmission to 4L80E, or is that only with the 6.5 turbo?
No you don't have to upgrade the transmission to a 4L80E.
I would consider it if I were you however.
Like Mogman said. you don't have to take out everything at once. but you can.
Having a park position in your truck to me is a big plus .
You can add a park pawl to your existing transmission if you would like.
With the 6.5N.A. / 4L80E you will get park as well as overdrive.
If you do choose to also do the 4L80E up grade you will need to source a trans controller and a wiring harness.
Was your engine toast when you got it?
Did you have a chance to drive the truck much before ?
I'm not sure what Tennesse is like and what your plans are for the truck.
When I changed from a 6.2 to 6.5NA it was a night and day difference for me. but I also switch to the 4L80E when I made the change.