I have a 3.2GHz, Radeon Pro Vegas 56 8GB, 64GB ram iMac Pro running High Sierra and Premiere CC 2018 and I imported some 4k 24 fps footage shot with a Sony A73 and it can not keep up in the timeline. It stutters and lags. I was under the impression that the iMac Pro could handle this? Is there something I am missing here? Thanks.