I've been looking for a used van to convert, comparing Nissan NVs, Promasters, and Transits. I have seen a number of NVs with 150,000+ miles that have had their engines replaced or rebuilt. I have not seen this with the other vans. Is this a general pattern with Nissan NVs? Is there a reason for it?
I don't have specific knowledge beyond the Nissan Frontier, but in general Nissan truck engines are as reliable as anything else out there. The V6 VQ40 has been made for so long that all problems were ironed out by 2010. I don't know much about the 5.6, but the Titan forums said that other than an exhaust manifold issue about 10 years ago, it was as reliable as anything else out there. It seems that there are less do-it-yourselfers/aficionados when it comes to Nissan so it is harder to know for sure.