lb7 and the 05 lly don't stand a chance against the 06 lly lbz,for starters the 06 lly and lbz have the 6 speed ally behind them,better fuel economy,better grade towing.i haven't heard any trouble from the lbz but have heard some trouble from the lly and lb7.i guess its just like anything else the longer the engine is around they'll improve it and make it better.i have a 06 lbz and a 05 lly,there is a world of difference not so much engine wise but tranny wise.
I think the lb7 are getting better mileage than the lbz. My cousin has an 07 and his dad has an 02. They work at the same place and the drive is the same and the 02 gets much better mileage. The 07 will definetly walk all over the 02. both have been good motors no trouble from either one. Just my .02 cents worth.