I’m having this same issue, using a Peplink 305 running 6.2.2 just installed this with new carrier 100mb circuit. Setup is ASA firewall connected to Peplink LAN port. Peplink WAN 1 is directly connected to carrier router. When laptop is directly connected to inside interface of ASA and the rest of configuration is as described above download and upload speeds are between 55 and 65mb. When I remove the Peplink and directly connect the ASA to the carrier router the down and up speeds are 92mb. Obviously the laptop, ASA, and carrier router are not the issue as this bandwidth degradation on occurs when the Peplink is in the mix. At this time I only have the one carrier connected and I used Drop in mode on the Peplink. The WAN 1 interface is set to Auto/Auto which is the only way it will connect to the carrier router and the bw is set to 100down and 100 up. I’ve tried to look via the CLI but so far have not found a way to look at the Peplink interfaces to see how they are actually running or if there are any errors. I too made no changes to the outbound policies or bandwidth limits.
Any thoughts would be appreciated.