My upload speed is suddenly very bad

Hi guys, I have been tackling this problems for a couple of weeks now and it´s driving me crazy.

Suddenly my upload speed on a Windows 7 desktop (Realtek NIC) has dropped down to such small levels that I can attach files in Gmail or even think about using dropbox. Many sites that depend on exchanging information in both ways also are barely accessible.

SYMPTOMS:
* Cannot attach "big" files in g-mail (takes forever, a 100kb file takes almost 20 minutes )
* Dropbox web interface takes 20 minutes to load
* Speed testing sites report great download speeds on the ballpark of 70-80 Mbps (my hired speed is 100 Mbps) but the upload test usually times out, when it doesn't it reports very slow number (less than 1 Kbps - I hired for 50 Mbps)
* some other websites are near impossible to use. Some are just fine (I can watch you tube and download perfectly)
* I´m in a home network, behind a router (Dlink DMG6661 - provided by ISP), all other devices on the same network are working fine (2 Windows laptops, 1 IMac desktop, couple of cellphones) with good upload speeds
* prior to the problem start, this same computer was working fine
* I had to user my laptop to post this message (this is ridiculous )
* The bad upload speed is also present in "Safe Mode with Networking"

WHEN IT STARTED:
Only two things I can pinpoint happened just prior to I noticing the problem
* Uninstalled Oracle VirtualBox 4.3.20 and installed Oracle VirtualBox 5.0.10 (this thing creates some virtual net adapters. Already uninstalled it to no avail)
* Heavy utorrend upload use (I though it could trigger some DoS protection on my router)

WHAT I DID TRY:
* several different versions of the turning off some of these: "Chimney Offload State", "TCP Window Scaling heuristics" and Autotuning, in various combinations
* Uninstalled VirtualBox e re-installed it a couple of times (it didn´t change anything installed or not)
* Turned off "Denial of Service" protection on my router (just to be sure I was not the router)
* reseting my network adapter as in : Resetting your network adapter in Windows 7

MY SPECS:
* Vivo fiber (in Brazil, optic fiber connection, supposed to be 100-50 Mbps)
* Reaktek NIC - D-Link router
* AV: Avast Free
* IP Config results below

Nothing works... I really don't want to format this one...

Help?


-------------------------------- ipconfi /all results:

Windows IP Configuration

Host Name . . . . . . . . . . . . : Titan
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Hybrid
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No

Ethernet adapter Local Area Connection:

Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Realtek PCIe GBE Family Controller
Physical Address. . . . . . . . . : F4-6D-04-AC-3D-7F
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
Link-local IPv6 Address . . . . . : fe80::5c3f:5bc:6f3a:5056%13(Preferred)
IPv4 Address. . . . . . . . . . . : 192.168.1.149(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Lease Obtained. . . . . . . . . . : quinta-feira, 24 de dezembro de 2015 11:
8:53
Lease Expires . . . . . . . . . . : quinta-feira, 24 de dezembro de 2015 23:
8:53
Default Gateway . . . . . . . . . : 192.168.1.1
DHCP Server . . . . . . . . . . . : 192.168.1.1
DHCPv6 IAID . . . . . . . . . . . : 301231364
DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-16-0C-DC-32-F4-6D-04-AC-3D-7

DNS Servers . . . . . . . . . . . : 192.168.1.1
NetBIOS over Tcpip. . . . . . . . : Enabled

Tunnel adapter Teredo Tunneling Pseudo-Interface:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Teredo Tunneling Pseudo-Interface
Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes

Tunnel adapter isatap.{5E2CE432-8920-49FC-891E-8FF30A257D66}:

Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Microsoft ISATAP Adapter #2
Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes