Except that the 350 is likely to do better on gas than the 4.3
That's why my dads '93 Suburban with a 350 got better gas mileage than my Blazer
I have a 2006 4.3 in a "FULL SIZE WORK VAN."
It is always loaded with my work stuff.
Around 1000 pounds of cargo at all times.
It gets a consistent 17 or so here in town, and close to 20 on the highway.
I think that is pretty good for as much weight as it is pulling.
I don't see where a 350 would get any better than that.
I have had "3" previous 4.3's before this one.
They all got about the same mileage.
oh.... and with a BlackBear tune....it runs fairly decent also.