According to the FAA ROD table, a 3.5 degree Slope at 150kt will be 925fpm. Passing 3500ft MSL, if you say the Vapp can get up to 160, it wouldn’t take much to get a VS over 1000fpm- but that wouldn’t be unstable in this case.
I guess the TAS and the slope is causing the higher ROD. Flap 3 wouldn’t be my first choice, but it’s doable, I’d think.
[img]blob:https://www.pprune.org/8ad432d7-3a41-4622-816d-11bb1857db4e[/img]
http://code7700.com/cdfa.htm