Hello Pete,
I'm sure someone will be along with some ownership views for you, but as an observation, unless the new C4 Grand Picasso has more power than the older model, then its unlikely to resolve your concern.
I can't be more specific as you don't tell us the exact models you are trying to compare, and what caravan you intend to tow.
When posting about cars its most helpfull to include
Make
Model & trim level
Body style (this can affect towing characteristics)
Year (different years can have different engine mods)
Fuel
Engine size
Power/bhp/kW (the same engine size can be supplied with differnt power outputs)
Mass In Service (kerbweight)
Max Towing Weight
And similar details are helpful for caravans.