Drive a Ford Transit and see whether you'd still want one of these.
We have a couple of the extended ton GMCs in the fleet at work as well as a 3/4 ton.
The 6.0 is indeed strong but overall driving dynamics are awful.
We have a single ton Transit and it drives ever so much better.
Bit of a weird driving position in that if you move the seat for a comfortable steering wheel reach the pedals seem way too close, but the thing drives really well and the V-6 has very good power, although you do have to let it rev in a way the 6.0 would never need.
Do NOT buy a Transit. You won't be happy with it. Their build quality is trash, and they are an absolute nightmare to work on. That, and the V6 engines have no where NEAR the power that a 6.0 Express/Savana has. No commercial van should have to be revv'd to the moon to make power, they need it down low where only a V8 can provide. There's a reason that GM has had such success with the G-van's for so many years. If this was a discussion about a Ford E-Series van vs. an Express, it would be different. However, working as a mechanic and servicing fleets of all varieties I can say with all confidence that you'll have better luck with an Express.
Before I get flamed, I will admit that NO cab-over design van is easy to work on. Not the Express, not the E-series, not the Transit. That just comes with the territory. That being said, the removable doghouse on Express/E-series vans make things a MILLION times easier when it comes to service. In addition, the Transit is notorious for front tire wear that even Ford can't correct due to non-adjustable camber angles. They use captured rear brake rotors that take way more time than necessary to replace (they also eat rear brake pads like I breathe air), whereas the brakes on G-vans seem to last almost indefinitely even in hard use. Parts cost is another factor: there isn't a huge difference, but in general the G-van or E-van will be cheaper to maintain than a Transit.
I will agree with fdcg27: the Transit drives better. That's ALL it does better. The Express/E-series vans may be antiquated, but there's a reason for that. They work.
If I needed a van for work, it would no question be a G-van. Econoline's are nice, but the modular Ford motor's are more complicated and take up even more room in an already cramped engine bay. About the only thing I can give to Ford is the transmission: The 6R line (based on the year you're shopping for) is a licensed ZF design, and it's rock solid. The 6L80/90 isn't quite is strong, but still more than capable from what I've seen.