They can tune it for the different turbo, for sure. Just be careful. The lly's don't like much above the 600hp mark. If I understand right, they start bending rods pretty easily past that. The 68 has the ability to take you above that.

I'm sure someone more knowledgeable, like like Silvergorillalml, will chime in. He is no b.s. and accurate.

When my lly was at its peak, I never even drove around on the big tune, just out of fear that I'd break something extremely expensive lol. Besides, it gets hard to put that power to the ground. Your rear tires will hate you

 

Really depends on your peak HP goal to determine what size turbo you should go with & what you use the truck for (daily driving, tow). From there we can direct you on what size you should get. Silvergorialla/ Nic would steer you towards Danville. If you tow heavy I'd stick with the 63mm, want a fun truck and don't tow that much a 68mm wouldn't be bad depending on your power level. If your wanting around the 600 mark mentioned above I'd look at Danvilles 65mm. Still have good spool and more on the top end of the 63mm. 65mm can support over 700 BTW

 

From everything I have read 68 is a little big for a daily driver, you wouldn't be happy with the spool up time if you are not into it all the time. It its mainly a drag or pulling truck thats a different story. Twin set up maybe?

 

Duramaxtuner has a few good videos on turbo sizing choices. They have one that compares stock, 64mm and 67mm that you might want to check out.