Was woundering because I read a few articals were they lower the compression, put a bigger turbo and up the boost. But they say the 21.1 compression is too high for a turbocharged diesel.

21.1 not too high for 6.5 in stock form or conservatively modded for enhanced power, how much power you are after will determine if you should lower CR. You can only stuff so much air in the cylinder before something has got to give, going with bigger turbo than what came with the 6.5, and not doing something about post turbo cooling of IAT will cause problem in long run. GM went with 21:1 for enhanced operability/starting/ and indirect injection needed it, going to larger turbo capabler of more boost and you will need to lower CR, IIRC Cummins & Strokes, & DMAX are in 17:1 window & run much higher boost 40+ psi I think. Go to the FAQs above and see what others have done for more power 200-240 Hp with mostly bolt on & reprogramming mods, if that isn't enough then the 18:1 CR is something else to get you into 300 Hp game