Question 6.7L Powerstroke as daily driver

I am looking to purchase a new HD truck. I tow a bumper pull travel trailer that weights about 10K lbs. I tow it maybe 6 times a year for a total of somewhere between 15 to 18,000 miles. When not towing it becomes a large grocery getter. I like to thought of having way more than enough power and torque but my concern is when I'm not towing and just doing short trips around town. Am I hurting the engine? or at these weights should I just go with a 7.3L gasser?

No you will not hurt the engine. Running less that full loads is easy in the running gear. You consider a smaller truck or a car for the grocery getting. Even with small loads your mileage will be considerable less that with a smaller truck or car. I worked in construction when I had trucks, from 1972 until 2022. I did not use a car for grocery getting and I paid for it. $$$$