so just my .02
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Being that we own 2 LB7's, 1 LLY, and 1 LBZ, I would have to say the LB7 might be my favorite of the bunch. Provided I will say that all of these motors are amazing, trouble free, and powerfull to boot. There isnt a bad one out of the bunch.
Now the LB7's obviously have their injector issues which is not a cheap fix if paying someone to do the job. However, the difference in fuel mileage is huge. If you are planning on putting on a ton of miles the added fuel economy is worth the issues. Our 03' has 320,000miles and runs like new. All while getting 21mpg mixed driving most of the time. My LBZ is hard pressed to get 18-19 on the same exact route. Usually more around 16-17mpg.
However the LLY and LBZ have been nothing but amazing. Dont see much notable difference between the two. Only issue ive had was the egr valve. Thats it. They are much more quiet and powerful than the LB7, but the LB7 has plenty of power IMO.
So basically, id say any of the three are a great choice. Just stay away from the newer DPF. And the allison 5spd (LB7) has held up very well when compared to the newer 6 speed too. Just my opinion and findings. Good luck on the search! If you are looking at any in CT let me know..
-Nick