I use Speedtest to watch my speeds and September 2016 over a period of just 1 day my recorded speeds dropped from 2.5 average to just 1.5 and have stayed there. At the same time I noticed the speed on my router settings had also dropped to match. When I called the tech line they reset everything and said it tested fine. But inside my house it still only tested at the 1.5. They sent new routers and sent techs out, they all say everything tests good and gave no reason for the drop in speeds. The tech did tell me they just added another customer in my neighborhood and the engineers likely dropped mine to add them......... I kept persisting in my calls and even had the area repair supervisors phone number, but a serious illness in my family made me push all this to the side. Now I am back on this again as my bill keeps increasing and my speeds are still too slow for a VPN (that I used no problem before). Why cant I get the 2.5 I recorded (and saved the test) or a good answer from Verizon? The area supervisor stopped taking my calls back the end of 2016. I have had phone service at this location 24 years and this same DSL since it was first offered over 10 years ago.
Try asking for help at the DSLReports' Verizon Direct forum with this issue: https://www.dslreports.com/forum/vzdirect
Chances are, a tool called ASSIA optimized your line down due to thinking your line was unstable. They just need to reset your provisioning back to 3Mbps (or ideally something better) and disable the ASSIA Optimizer.
This is what happened the first time, the online techs reset my provisioning which didnt put my speeds back where they were, then it happened again. Online techs fixed the provisining again and it has not changed since, but my speeds have never gone back where they had been. Downstream rate has stayed at 3360Kbps and downstream at 863 since then, but speeds still only test at 1.5 using Speedtest.net. My concern is, the first couple of techs that came to my house didnt seem to know much about how DSL worked, had trouble hooking up their equipment (this was at the end of the Verizon labor strike). And I'll try the link you offered in your reply, thanks.
So if your sync speed is at 3360kbps but you're seeing 1.5Mbps, there's a few possibilities here.
1: They adjusted the sync speed on the line card but did not update the profile on the Juniper ERX BRAS which aggregates all of your Internet traffic back at the Central Office.
2: You are on a Litespan 2000 DSLAM and the incorrect provisioning profile is applied to your line. The Juniper ERX may have a 7.1Mbps profile applied when your sync is at 3Mbps. This will cause a buffer overflow issue causing inconsistent speeds. Since your uplink speed is 863kbps, you're probably not on a Litespan 2000. More than like you're on an Adtran TA1248 (hopefully not) or an Alcatel 7300.