swap

I have a 97 k2500 4x4 auto with the 6.5, and I'm toying with the idea of swapping it for a manual. One reason is it seems to not want to shift into overdrive sometimes. It's a stock transmission with 270k on it. I don't know what maintenance has been done to it. Thoughts?

I am needing to know if it is possible to swap a 5.3 from a 02 1500 surburban to the 8.1 or at least how difficult it would be if it is able to be done.