[ALL] Desperately need advice or help re my Shaw BB50 connection.

I've recently (this week) developed an exceedingly weird issue regarding my download speed on BB50. Let me first describe my setup. I use both my Shaw IP's. One of those IP's is connected via ethernet cable to a freestanding laptop which I will call DMZ. In other words, it is IN NO WAY related to my second IP, which houses a LAN served by a DD-WRT hacked d-link router. In other words, two discreet systems, which could be at opposite ends of the Shaw geographical area, tho' both share the 50.71.xxx.xxx address range. About a week ago, I noticed on both DMZ and LAN, a sudden and severe drop in download speed along with a massive increase in latency and ping. I quickly checked on the Shaw Speed Test and got down speeds in the 4 - 1 mbps range. Insanely, my upload speeds, on all the test sites, was just below 3, iow, "normal" Assuming that this might be a mere problem with the speed test, I checked my ACTUAL download speeds using Astraweb, which normally gives me a tad more than 50 mbps. Now, it was sending to me at 3 or 4 mbps at best, on both LAN and DMZ. Finally, I decided to double check my catastrophic drop in speed by using the new dslreport speedtest. And here's where it gets spooky. The DSLreport test instantly gave my my full, wide-open 55 or so mbps. Again, tho I hate to repeat myself, on both DMZ and LAN Now, I began thinking magically...Maybe the router was "somehow" interfering with all the modem's ports or the DMZ machine, so I shut down the router and physically removed it from the modem. No change, DMZ speed remained awful (1.6)...and, just to drive me nuts, the dlsreport test showed a perfect 55 or so. During the course of the week there have been two brief periods (a few minutes), when my bb50 speed returned to normal. I really need some help on this. What could possibly account for this issue? I think I've proved it has nothing to do with the router and the LAN. If it's the modem itself, how come I can get a full 50 mbps on dslreports (and several other,one of which is IN MY CITY) test sites? The first thing that came to my mind was that I was being throttled...but that makes no sense, and I believe Shaw when it claims they never throttle downloads. Further, I've never, not even once, exceeded my monthly allowance. One final point. I had a support visit from a (nice guy) technician who insisted that my problem HAD TO BE at Shaw's end, something to do with routing, whether dns tables or whatever. (In other words, it's "as if" once requests get past the gateway, they split and most of them enter screwed up routing tables) But, as you probably can guess, Shaw absolutely refuses to connect me to their network people and, hahaha, every time I use the word "routing" on the phone or the concierge chatline, the first line kids tell me that they don't support routers. It's getting into Kafka territory. Please help. Any further information requested will be immediately forthcoming. (And, finally, should I have posted this elsewhere?)