Linksys Wireless Router :: WRT54G / Switch From G To N Causing System To Freeze Up?

I work from home on a Lenovo Laptop.  I connect to my work network, and ultimately to a midrange ISeries.  For the past year I've had no major problems with my Netgear Linksys WRT54G.  I switched to a Netgear N300 last weekend because my husband's desktop was having a lot of issues.  His connection is much better now.I'm able to connect to the internet with no problem, and I can access my company network & email pretty well.  But, when I log on the ISeries it slows to way less than a crawl.  According to my netwok icon, the connection is anywhere from 104 to 130 MBPS at any given time.  But it freezes up so badly that it takes about 20 - 30 seconds just to type each letter, or to go from one window to another, or just to move the cursor down one line.  It's infuriating.  Every once in awhile if I disconnect and reconnect it works almost normally for awhile, but eventually slows down almost to a stop again.  I actually worked for about 90 minutes the other day with no problem before it started acting up again.  When I put the old G router back it works fine again.   My laptop has an Intel(R) Centrino(R) Advanced-N 620 wireless adaptor.  As long as I don't connect to the iseries, I have good speed and no issues with the internet or work intranet.