hupp3l...
OK... Here is my suggestion... you might not want to do it because it is a pain... but it will narrow it down.
Set everything back to default... all your settings, etc.
(Make sure your routers are set to factory default)
Check the settings on your NIC card... if you haven't already... it should be set to auto / full-duplex
Put you Verizon supplied router in-line and test with it... you should be getting your advertised speeds here!! If not, then you need to get Verizon involved.
Remove the DLink and put your Linksys in-line and test with it...
If the Linksys tests the same as the DLink... then start adding from there...
I had to do the same thing on the wireless side of my DLink DI-624 this past week. I tried everything and someone suggested I go back to square one... didn't want to... but I did and everything is back rock solid.
Please let us know what you find out.
Cheers,
Ronnie