Originally Posted by SMB123
You are entering an area of chasing the dragon. Tread carefully and don't get bit.
Yeah absolutely this is something to keep in mind especially with drive trains of the OP's era.
Re-gearing is probably the least expensive and easiest thing to do--within reason of course. You'd want to get recommendations based on your engine HP and most efficient RPM's.
There are "truck/RV" cams available that re-shape the torque curve but that's not an easy thing to add----depending on the van's current mileage this might negatively affect the engine's longevity.
It would be tough upgrading the 5.8 and not break the bank although we have no idea to what dollar amount that refers. IOW there's not a lot of cheap and easy DIY mods one can do.