Originally Posted By: 14Accent
The 3900 has AFM as well as VVT, which adds another layer to things that can go wrong. The 3500 has VVT only, and they're mostly bullet proof. Intake gaskets are no longer an issue, the coolant now flows through the coolant crossover which is on the passenger side of the cylinder heads. Those gaskets DO leak, however it's much less involved to change them, somewhere around 2.5 hours vs. 6 for a LIM job on a 3100/3400.
I've read on here and other sites that the LIM gasket issue was pretty much resolved by 2003/2004 for the 3100 and 3400 series motors. How does the problem perpetuate on a different engine that came into existence in 2004, when the problem was supposed to be fixed? If the LIM gasket was really an issue with the 3500, I don't see how it wouldn't still be an issue for the 3100/3400 series motors.
As for buying the Lucerne, just be wary of the 4T65E. Drop the pan and make sure it has had new magnets installed per TSB 08-07-30-040C. It should, being a 2011 and all, but I would still check. I also added a few extra in my 4T65E, just to be safe. While you're at it, replace the filter and use Valvoline Maxlife ATF. I have found it to work really well.