I just bought a LLy 2006 sierra. I did not realize there were two versions of
the Duramax diesel. Will a performance chip like bullydog pup bring my LLY up
to the performance of the LBZ. also, does anybody know exactly what makes these two engines different that gives the LBZ added HP.?

Tuning is the only difference. I can dial up both to over 500hp, or I can take an LLY and make it LBZ spec.

How come GM claims these changes made the extra HP improved block casting,new piston design,thicker connecting rods,revised cyl. heads,higher psi. fuel pump & 7 hole injectors. im no mechanic but these parts cant be changed with a tuner can they??? im sure you can get 500+ hp out of either engine but they are not the exact same inside.:)

That was the change for the 2005 LLY. The 2006 lly is a lbz. It is just a detuned lbz