2019 and up are the longer xt versions. You can now easily reach the u-joint grease nipples with any grease gun and have more room to work on the same. They added some heat shields to protect the bed from muffler heat. Better a-arms for clearance to just name some that I know. I never owned a 2015 model but we have a 2018 and a 2020 model in the family stable.Can you please tell us more about these improvements? What did they do?