Okay you've got me convinced, going to make a toy with the Duramax and put a jku stretched body on the 1 ton frame, a 6.1 is basically a better 5.7 isn't it? And where would be best place to get one reliably
Surprising lol
Yes and no. They are in the same family, but the 6.1 was designed from the outset to be a performance engine, forged crank, better heads with bigger ports and valves, better intake manifold, much more compression and cam, piston oil squirters, etc (the 5.7 was not). Can you put the 6.1 in your truck? Absolutely. What you need to decide is how much of the engine you actually wanna use. There's cheapest/easiest, more involved, then much more PITA & expensive.
Cheapest/easiest: 6.1 short block with 5.7 heads. Everything bolts back in like factory and you just need to pick a cam and get it custom tuned.
More involved: 6.1 long block. Now you have D shaped exhaust ports to contend with as well as larger intake ports to adapt to. Have to either find headers or alter manifolds to work on the exhaust side. Need adapters to use your stock intake manifold on the 6.1 heads. Stock intake becomes the choke point on the engine.
Much more PITA & expensive: 6.1 long block and intake (or some version of car intake manifold). Requires altering the accessory drive to fit front facing throttle body and requires conversion to electric cooling fan to get rid of clutch fan. 6.1 intake will then bolt right on; 09+ plastic intakes are shorter and won't clear the temp sensor without spacers (but are superior to every pre-09 plastic intake and in most cases match or supercede the 6.1 intake).
Used 6.1's run about $4000-7000 on average depending on mileage and who is trying to gouge the price; they're also getting harder to find and people want more for them.
Easiest method for more power while keeping stock packaging but will probably eventually blow up your RFE: take stock 5.7 block, have stroked to 392 (this gives you forged internals). Have stock heads opened up P&P and big valve. Have cam made for boost application. Buy 04-08 Ram Procharger tuner kit. Get it tuned. Have fun with it while trying to decide where to get your next trans or if you're gonna try the ZF retrofit.