I have a 2020 with the V8 and have never had any problems with power or going down grades. I do all my towing in "S" and "Tow Haul" modes which makes a big difference, as does having the larger drums with the 5.2k axles. Getting the trailer controller dialed in correctly makes a big difference, too... When it comes to braking, you don't have the larger margin of safety that 3/4 ton trucks do so everything has to be dialed in.
I'm with you on a diesel option and would buy one the second it hit the market. Not a fan of *any* of the modern big 3 diesel options and wouldn't even consider one.