I have recently purchased a 2018 Hyundai i40 Tourer diesel with an automatic gearbox. The car has done 42, 000 miles. On two recent occasions when I get into the car, start the engine and then move off the car has juddered as if the gearbox is slipping. Once the car has travelled a mile or so the issue does not repeat. Only does it when stating from cold. This issue is intermittent. Also, when I am travelling along if I touch the brakes the gearbox drops down either one or two gears and can result in the engine revving up to 3,500rpm. This issue is present all of the time when the brake pedal is pressed. Can you tell me if this seems to be a fault with the gearbox? I bought the car from a Hyundai main dealer and with an 18-month warranty. I wanted to make sure of the situation before I approach the dealer if there is indeed a fault with the gearbox. The issue was not present when I bought the car but it started after about four weeks after the purchase.