I as well as others can and will tell you,, do not get all wrapped around the axel with "Chips" or "Reflash" or add on Tuners. Although they do add substantial powwer to the ass end of a truck the cost does not stop there! keep your wallet handy and work any overtime you are allowed or even pick up a second job. Your gunna need it!
My dodge and i refer to the cummins engine as opposed to the 6.5 platform makes increadable power with a diablo preditor and a power puck stacked and just on econ tune. But ,,, here comes the get your wallet ready part... You better beef up anything around your truck that is going to receive more power. I.E Tranny, Inner cooler ( Which the 6.5 lacks) Getting more cold air, and will never achieve the power the others have because of this, and injectors that can deliver more fuel as needed. everytime i take the dodge to the dealer when it decides to go south before me its 900$ Min. injectors and so on.
Do the basic mods for your chevy and drive it like it is intented and not peel off 1/4 inch of rubber on burn outs and boost launches and youl be fine. In fact good luck getting tires to break traction on dry pavement for a burnout anyway. Nearly impossible. to reach 250+ HP at rear wheels on the chevy 6.5 you better pull out some serious cash and invest and youll always be turning a wrench of somesort. Now the newer Gen diesels are delivering 325+ RWHP outta the assemb ly line. and you can keep adding to that with a severe cost. I know for fact I lived it!!
the best MPG your gunna get outta the 6.5 platform is doing maintanance mods as awell as longivity mods and wearing light shoes to keep off the pedal! when some one says "Smoke" tune, smoke is almost always associated with trouble! Looks cool in certain applications but in the long run, it aint cool to be broke and have no money because your power greed got you in debt up to your anus hole! heavy loads??? wanna haul Heavy? 15K plus? get a newer diesel that can handle it. The 6.5 is a mid range work horse and that is all it will ever be IMHO. But serves its purpose flawlessly if maintained and taken care of like a fine woman. make her feel good and she will return the favor! Coke her all up and on day 4 she is gunna crash hard and lay there like a useless, expensive projecT. Just my .02
Be the smart Kid Hugh. While your friends are always turning wrenches, ( BTW, with a 6.5 you will have to turn wrenches! Welcome the the world of the 6.5 Detroit Deisel) make your truck make you money and not cost you! When your friends tear the teeth outta there trucks, you will roll past with a load of wood, or pulling a landscaping trailer on your way to let your chevy provide you with income instead of robbing you of it! My Moral of the story

Best wishes young friend you will no doubt learn alot about diesels with a 6.5 without losing or gaining gray hair.