We own two 2019 Silverado 1500s. My wife's is an RST, mine's an LT, (I am I like chrome guy). Both have the 5.3L engines. We both use mid-grade Shell or BP gas. We get our best MPG from these two gasolines. As both engines appear the same, the RST will outperform the LT. In the following, I am referring to the **** on the top left of the dash. Left is for tow-haul and right displays a green flag in the display in front of the steering wheel. Both trucks are in AUTO drive, With the RST in normal, (no green flag), it accelerates better than my LT with the green flag on? Is there a different chip in the RST? I want my LT to perform as well as the RST if that's possible.

 

Run it in 2 high when it's not slippery like snow. Auto mode locks the front diff so transfer case can engage 4wd when the rears wheels slip. In auto the drag of the front diff. being engaged will slow you down and suck more gas. My Tahoe only sees auto in winter with snow road or when my wife winter drives it.
Check the manual.
Both motors are the same, auto transfer case selections / programming may be the difference.

 

I have a 21 High Country Silverado with the 6.2 and 10 speed. My **** is tow/haul to the left and Sport and Off Road to the right. The green flag indicates you are in Sport mode. It changes your shift points and burns more gas. I agree with the previous poster and you should be in 2WD in anything but slippery winter conditions.

 

Check your RPO codes. The RST may have a lower geared rear end.
I also agree on keeping in 2wd unless slippery conditions.