I've been seeing your posts on Masto, but I guess I'll reply here.
I don't know what printer you have, and I don't know if the feature works for all printers, but could you try and use PrusaSlicer to visualise the print where the issue presents itself. More specifically, you could get some interesting data from the "actual print speed" view. That way you can see what speed the printhead reaches.
However, based on your description:
- when the printer reaches high print speeds you get delam
- slowing down the print head reduces (but doesn't eliminate delam)
Could you be reaching the limit of what your printhead can melt? Would it make sense to calculate the actual flow through your nozzle at those high speeds? Finally, how much part cooling do you have setup? Have you tried a skirt to keep the temps more consistent?