MB8600 WAN LAG with Asus RT-AX86S

I recently replaced my CM1000 because I was bumped to 1.2Gb service. I replaced it with an MB8600 because my AX86S can only do >1000mbps if you do a LAG with ports 1 and 4 (no 2.5Gbps port.) I was able to get the modem to come online as DOCSIS3.1 (all blue LED's) and my router shows the LAG is connected at 2Gbps. However, I can only get ~800mbps down no matter what I do and it varies from 650-800, this is tested directly from the router to the modem in the ASUS GUI. With my CM1000 I was able to get 940mbps consistently.

Is it possible that my modem isn't provisioned correctly? I have seen others that were able to get 1400mbps with their 8600's.