I'd advise you to take a look at a few sites of Verizon's sites on the net as they might have a guide on there, or even contact one of their support workers and let them know your situation. Perhaps they've had this problem before with another customer and can help you find the best way to remedy the situation.
Here's the URL for that model of yours, look in the documents section: http://www.actiontec.com/support/product_details.php?pid=188&typ=doc
If not, I did a simple search and found another site which might help you out - it has lots of reviews on extenders so take a look at: http://www.wirelessrangeextenderreviews.com
The trouble is I don't know if you are having a problem with your router because its slow in general and it has a problem, which means buying any more equipment might not remedy your situation