That sort of sounds like one of the symptoms I had when my wastegate was shot. For example, I was on the freeway and changed lanes to accelerate past another car. There was just the smallest bit of incline to the road, I would not even call it an uphill section of the road. When I pushed the accelerator the car started to pick up speed, but then just didn’t go any faster, even when I pushed down a little more on the pedal. It felt like I was driving through molasses or something, then I pushed further on the gas ...... and “Do De Doo” the dreaded half engine light and limp-mode. Funny thing is, this weird molasses moment, only happened like twice. The rest of the time it seemed to pop right into limp mode much sooner almost as soon as I tried to accelerate on an incline. The ECU wanted boost, and it just wasn’t there.
Thats why I doubt I’m being very helpful. Your turbo is probably fine, but it sounded eerily similar to what mine did a few times. Might be worth checking out if you can’t figure it out. I could still hear mine spool up fine, it just wouldn’t make enough (or hold any) boost.
Good luck! I’m curious to find out what it is.