Anyone tow with a Kia Sportage 2 litre diesel MHEV

I have a 2019 Kia Sportage 2.0 GT LineS 2.0 litre diesel mild hybrid 8-speed auto, AWD

I have a problem with my 8-speed auto transmission that only occurs when towing my single axle Elddis caravan, max permissible weight 1500kg. Without the caravan the car is great, with the caravan it changes up through the gears until it gets to 4th but then hangs in 4th gear until the revs get to 3200rpm or more before it’ll change up to 5th  This equates to more than 60mph so not ideal when towing!  Luckily I can override the auto box with the + flappy paddle, and when I do so at about 2200rpm in 4th the dash display comes up with 6 in green with an up arrow indicating that the car thinks it should be in 6th gear.  Once there it seems quite happy to cruise along at just under 2000rpm on the flat at just over 50mph, and similar revs in 7th on dual carriageways at 60mph.  Without the van on the back and driven gently it generally settles around 1600rpm in each gear on the flat, so I’d expect more revs with the van on the back, but not the reluctance to change up out of 4th and sometimes 3rd too.  The car changes down perfectly with the van on the back, its only up chages that are affected.

The towbar fitter used a Right Connections electrics kit, and I also had this make of kit on my previous car; a Ford Kuga Mk2 2.0 TDCi with the Powershift gearbox and AWD with no gear changing issues at all.  Right Connections say that their box of tricks doesn’t write anything to the car’s systems, and there are no software alterations to the car after fitment, unlike the Kuga where some re-programming is required, so I can’t really see that being the problem. The car has been back to my local Kia main dealer who can find nothing wrong with all software correct and up to date, and Kia technical claim that they have never seen this before.  If I plug in my towbar mounted bike rack the car drives normally.  Anyone else tow with one of these and had any issues??