should not hear the BOV under steady throttle... but after letting off, ok.
when you say no mods - no mods from you, or, you bought it new and you KNOW there are no mods?
Normal mode is disgustingly lazy in the Rap. Especially early production ’17’s. A combination of programming commands the truck to stay in the gear it’s in under most conditions, including part throttle in higher gears. The first time this happened to me, I thought I broke something. I went to merge on to an interstate from a 35mph exit and the truck was in 8th gear, would not downshift. I floored it and still no downshift but FULL BOOST for what seemed like an eternity as it waddled its way up to 60mph and I just hit the brakes waiting for a gap.
There was a TSB to address ‘harsh’ shifting that fixed this on my truck.
This is why I asked about normal drive mode. It can sometimes fool you into thinking “WTH? Where’s all my power?”
use sport mode and see if it behaves the same way.