We're happy to help but we'll need quite a bit more info.
Please review the read Me Before Posting sticky thread at the top of the PD17 forum, then run the DxDiag test and attach the results. That will tell us the condition of your computer, and we'll be able to see if your important drivers are up to date.
Typically, if people people see sluggishness it's when previewing clips on the timeline, but from your description, your problem is when scrolling through the transitions in the respective libraries.
Could you use ScreenRecorder and capture what you're seeing? You can upload it to YouTube and paste the link in this box when you reply:
Or upload it to cloud folder on Google Drive, OneDrive, etc. and just paste the link to it.
YouTube/optodata
DS365 | Win11 Pro | Ryzen 9 3950X | RTX 4070 Ti | 32GB RAM | 10TB SSDs | 5K+4K HDR monitors
Canon Vixia GX10 (4K 60p) | HF G30 (HD 60p) | Yi Action+ 4K | 360Fly 4K 360°