With DLMs logic being undisclosed and what seems dynamic I thought it could be caused by the cap.
My plan was/is to get the downlink cap lifted first then address the uplink if the issue persists.
You have a very good speed based on the attenuation. DLM should with time adjust if the line can handle it (we're talking like 4 weeks+ time wise).
In my view getting the ISP to reset DLM is quite pointless, as whatever made DLM apply the speed cap initially is probably still there, so it will just re-cap. If the line truly is fine, DLM with time will adjust. I am by no means saying it does that quickly, often between 2 weeks and 3 months.