I towed a 16-foot pop-top with my 2018 Isuzu MU-X in a 29 km headwind and was in fourth gear for 300 km. If l used fifth gear, it would drop back to fourth. I was hoping to upgrade to an 18-20 ft. van shortly, but this a joke. Can the turbo be tweaked up or what is the problem. The vehicle has only done 1400 km.
It’s not a good idea to be towing in fifth gear into a head wind or uphill, or in other adverse conditions. If you do the gearbox will shift back to fourth, or lower if need be. I wouldn’t be too concerned about towing a larger van, providing of course it doesn’t overload the MU-X. You could upgrade the turbo with a chip or other device, but in my view you’re risking trouble by doing it.