adjustment clips slow davinci and the framerate

hi all

ive been pulling my hair out over this for months.

once i place an adjustment clip in a video track all the clips below are slowed down on playback in the editing page. the framerate drops to around 9fps, but goes a as low as 4fps.

also if i adjust the adjustment clip - move it shorten it lengthen etc - davinci hangs at the same time the PC fans spin up to what sounds like maximum - i cant see what the rpm is as davinci dominates the PC making it all hang.

after several months of trying to sort it myself by reading thread and watching videos, i cant work it out.


all advice appreciated.

thanks


PC
Windows 10 - up to date
amd ryzen 7 5800x
b5550 plus wifi
ddr4 64gb
geforce rtx 3060


DavinciResolve 18.6 - free version (if i can work out the problemst, i want to buy studio)
render cache - smart
working folder is on desktop - c drive
cache files are on internal d drive - DNxHR SQ
all media is in the working folder then dragged to media pool
all media has been optimised.
mix of gopro, mp4, jpeg. various sound files mp3, wav
gopro files are handbraked as they were so choppy , it was unworkable.