Take it back for adjustment. One of the mysteries of bikes is that when the cable tension is "perfect", the bike will shift quickly and smoothly on a work stand, yet still hesitate or hang-up when pedaling hard out on the road. Sometimes a tech needs to "road test" a bike to get the shifting dialed in.

Bikes shift best when you have a straight chain line. Because chain stays have gotten silly short over the past two decades, a truly "straight" chain line is limited to just a few gear combinations.

For example, when you are on the largest three cogs in the back, and the small ring in front, you have a straight chainline. But, if you are on the largest rear cog, and then shift to the big ring in front, your chain is now at an angle, making shifting more difficult.

So, if you are on the large cog and small ring, first shift over to a middle cog. Then move to the large ring. And, shifting works best when you are pedaling smoothly, but lightly. If you are half-way up a steep hill, and putting maximum pressure on the pedals, you have waited too long. Gotta shift before things get tough.