Premier Pro scrubbing/performing slowly with 2019 Imac Pro and Catilina OS

I have had issues with editing video in Premier Pro with either 2019 and 2020 versions on my Imac Pro. I cannot scrub through footage and have been getting dropped frames in playback. I am editing 4k footage shot with Sony A7III and A7SIII and should be able to scrub through this video without issue with this Imac. I currently have 3.6 GHz 8 core I9 - 64GB RAM Radeon Pro Vega 48 8 GB 

     Any suggestions appreciated!