Rough shifting

Just this morning I noticed that the first shift my automatic transmission makes is not so smooth. Almost like I’m getting a slight shove from behind. Repeated at every stoplight. I know I’ll be calling the dealer tomorrow, but am hoping to get ahead of the curve and be prepared for what it might entail.

Car info please: Make, Model, Year, Mileage. Also if you can describe any thing that was different this morning besides the car behavior, was it cooler than usual, Did you jyust replace a battery and drove this morning, did you park on a gradient (which you normally do not?) etc.
The first thing I would check regardless of the above is the level of Automatic Transmission Fluid.

Sorry, I thought when I entered that info before it would be visible to everyone.

2008 Chevy Silverado, 6 cylinder, about 50K. No on everything else, including the fluid, which I will check right now.

Fluid is OK.

You have owned this vehicle for some time and this is the first manifestation? Reason I am asking is that to me the 1-2 upshift on Silverados is harder than other similar sized vehicles in my experience.

It has always shifted hard when the towing/hauling feature is engaged. But not otherwise, and yes, this is the first time I noticed it. Also I am the only owner of this truck since it was new.

A soft 1-2 could be an issue with the 2-4 band or band servo or it could even be a line pressure issue. Let me know what the dealer says. Is it still under any kind of warranty??