Typically Verizon support would have you check the RWIN setting on your PC/laptop.
Go here to check:
http://www.speedguide.net/analyzer.php
Default TCP Receive Window (RWIN) = 65700 (You want to look for this line - as long as the number is in that general range you're fine; if you're on Windows 7 you can't change that setting anyway so it's kind of a moot point for them to have you check it for the most part)
You can try running the Verizon Speed Optimizer but that hasn't done much for me.
http://my.verizon.com/micro/speedoptimizer/fios/NonIE/Default.aspx
Most any setup can easily handle 50/25Mbps. You do want to test your speeds while connected through an Ethernet cable as opposed to Wireless though to get a more accurate result.
Do you know what they've tested/replaced at your house as well? (ie. replaced the router, ONT, etc.)