I have heard that on some frontiers that the angle of the drive shaft was off and would cause similar symptoms to what you are describing.
There are also claims of the tire needing balancing, check out this link:
http://p085.ezboard.com/ftunfsfrm41.showMessage?topicID=782.topic
Here is a website with TSB on the 2005 frontier:
http://www.nissanhelp.com/Bulletins/Frontier/2005/1.htm
There are also claims of the tire needing balancing, check out this link:
http://p085.ezboard.com/ftunfsfrm41.showMessage?topicID=782.topic
Here is a website with TSB on the 2005 frontier:
http://www.nissanhelp.com/Bulletins/Frontier/2005/1.htm