A mem upgrade should definitely help. Do you have any other stuff such as IPSEC runnin on the same router ? Attach a sh proc cpu when its 99% on your next post.
But the catch is, that NPE 150 does not support more than 128 MB. Atleast thats what I think after reading this link.
http://www.cisco.com/en/US/products/hw/routers/ps341/products_installation_guide_chapter09186a00800a9348.html
Your current 128 MB is made up on 4 32MB SIMM chips. You need atleast a NPE200 or higher to support 256Mb ram.
Meanwhile you can use the 3660 to support this configuration, make sure you got the right T1 interfaces on the 3660 to swap the T1s.
Sankar Nair
UC Solutions Architect
Pacific Northwest | CDW
CCIE Collaboration #17135 Emeritus