TR196

I'm looking at 2008 Silverados and am hoping to geta little help with the different engines. It looks like GM has 4 different 5.3 engines available (if my web info is correct??); iron or alum flex fule (LMG, LC9)and iron or alum non flex fule (LY5, LH6). So here's my questions;
Why the iron and alum versions?
Which is better or proven design? durability, gas mileage, etc
Is there any reason to stay away from the flex fule engines?

Thanks for any help!

Gman

We had a problem with our first 07' Tahoe with the 5.3 flex-fuel engine. It developed a tapping noise at 300 miles and GM's engineers couldn't figure out the problem. GM ended up buying the vehicle back and we ordered another 07' Tahoe with the sameflex-fuel engine. The second Tahoe now has 25,000 mileson the clockand runs just fine with no problems. I know this doesn't answer your question but all engines are not perfect once in a while a bad one comes along. For my money anything Chevy makes is good it's like anything else roll the dice and take your chances. I will say whatever engineyou end up buying GM will stand behind their products.