Which newer style diesel should I swap in my 97 sierra 2500 6.5 4by4? I was thinking a 07 duramax but don't know what is involved. I love my truck and want to keep it, but I want the newer power. Thanks!

how about a cat engine? it would be unique and craploads of HP and TQ

Putting a duramax into an older body it a very involded task. Look around on here and you will find that a few guys have done it. I on the other hand sold my 95, bought a 01 and droped in a dmax in 2 weeks. There is also info available on putting in a cummins, this swap will be easier because of the electronics.