The problem started a week ago. I have Dell desktop PC, with Windows XP, router connected via wired (ethernet) cable. I have 50/25 service. My upload speeds are very slow, most speedtests show great download speeds, but terrible upload speeds, like this.
http://www.speedtest.net/my-result/3570061501
Basically I'm only doing around 1mbps upload. I have tried everything, resetting the router by holding down the button in the back, as well as unplugging it. I also reset the ONT. I also ran the Verizon Speed optimizer on their website, rebooted the machine, problem still persists. I called them, they ran tests on the line, and said it was working fine. The odd thing is Verizon's own speedtest shows I'm getting proper upload speeds. Usually says 60/30, which is better than even 50/25. But once I got to Speedtest & other servers, the upload speed is very slow. Problem started last week. I'm wondering if it had to do with removing the Verizon In Home Agent program which kept giving me errors. Though on the phone Verizon told me that Fios services do not require any of their own software to run on my machine.
Verizon's own diagnostic test gave me these results, which I do not understand.
Checking for Middleboxes . . . . . . . . . . . . . . . . . . Done
SendBufferSize set to [261360]
running 10s outbound test (client to server) . . . . . 36.26Mb/s
running 10s inbound test (server to client) . . . . . . 43.82Mb/s
------ Client System Details ------
OS data: Name = Windows XP, Architecture = x86, Version = 5.1
Java data: Vendor = Sun Microsystems Inc., Version = 1.6.0_17
------ Web100 Detailed Analysis ------
Client Receive Window detected at 1045440 bytes.
2.4 Gbps OC-48 link found.
Link set to Half Duplex mode
Information: throughput is limited by other network traffic.
Good network cable(s) found
Normal duplex operation found.
Web100 reports the Round trip time = 13.72 msec; the Packet size = 1460 Bytes; and
There were 488 packets retransmitted, 2718 duplicate acks received, and 2872 SACK blocks received
The connection stalled 1 times due to packet loss
The connection was idle 0.21 seconds (2.09%) of the time
This connection is sender limited 66.25% of the time.
This connection is network limited 33.75% of the time.
Web100 reports TCP negotiated the optional Performance Settings to:
RFC 2018 Selective Acknowledgment: ON
RFC 896 Nagle Algorithm: ON
RFC 3168 Explicit Congestion Notification: OFF
RFC 1323 Time Stamping: OFF
RFC 1323 Window Scaling: ON
Packet size is preserved End-to-End
Server IP addresses are preserved End-to-End
Information: Network Address Translation (NAT) box is modifying the Client's IP address
Pingtest results

I haven't gotten any answers. I may just try re-installing the "In Home Agent" and see if that fixes it.