Had my 21 RST 3.0 for 6 months, just under 6k miles. Love it so far. I have had really no major issues so far. A couple small things...mainly being the infotainment system is glitchy when trying voice to text and with syncing with my samsung galaxy. The only other issue is that after the truck has been sitting in the heat, occasionally the AC won't come on when I start it. I have to turn off the AC and turn it back on once, sometimes twice, before it kicks in, this only happens occasionally. Haven't been back to the dealer since buying it, but I am going to get the oil changed and I'll mention it at that time
For MPGs I am getting typically 20-22 for city driving. I was getting 33 with a tailwind down the VA eastern shore going around 60. More typically its 27-29 on the highway averaging around 26-28 for a 600 mile tank when it is mostly highway, and the manual calculation at the pump usually beats the computer by 1-2 mpgs. I am not a particularly heavy footed driver.
Just towed a 6.5k lb travel trailer this past weekend, and I was averaging 13-14 going 55-62. Had no issues with towing either, felt like I had plenty of truck for the trailer.
Overall, I feel like it has plenty of power, its not as quick a my MINI Cooper S, but quick enough for getting on the highway and passing if needed. No regrets so far.