HP is good. I got the 6.0PSD and wish for more. Like others say it depends on what the van will weigh. At least you wouldn't be sorry down the road if you found a V-10. BTW the new Ford diesels are very very quiet. At least the 550's are.
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2006 Ford 6.0PSD EB-50/E-PH SMB 4X4 Rock Crawler Trailer
I agree with carringb. I've driven 4x4 vans with the 5.4, and it needs more power. Even with 33's and the proper gearing. The 5.4 is an extremely reliable engine, but a loaded van needs more power! And resale value will always be higher with the larger engine.