Zoe went through the same exact thing, for about a year. She now loves "letting go" on hills (and singing Frozen while doing it)
I've been riding a bike for 6+ decades and I'm still scared of fast downhills. (I don't do roller coasters either.)
Completely unrelatedly, but noticing that Abi pokes in here too, I thought she might be tickled to hear that the bright red Rootstock Racing T-shirt that I got at the Pa Tpk tunnel rogaine / adventure run several years back has been proudly displayed in most of the states of the USA and most of the provinces and territories of Canada, right up to the Arctic Ocean at Tuktoyaktuk. Although since it was 42° in August at that particular stop, it might have been covered by a sweatshirt at that point.
That's awesome, o-maps! Feel free to pass along pictures :)
Glad to hear that we're not the only ones with that struggle!
We are expecting him to be at that level before kindergarten.