ShadowProtect backups of Exchange server slow over time

We have a Dell PowerEdge T610 with 2x 2.4 Ghz quad core processors and 16 GB of RAM running Exchange 2010 SP1 for about 40 mailboxes on Windows Server 2008 R2. We are using ShadowProtect 3.3.0.16 to back this server up. When server starts up, backups run fine, but initialization time gets longer the longer the server is up. This time since server was rebooted, backup initialization was at 25 minutes after 5 days, 90 minutes after 9 days, and now on day 11, initialization took almost 3 hours on the last backup. The task status on ShadowProtect server shows initializing during this time. Once initialization is done, backups still only take a few seconds like normal. Might this be a VSS issue and is there something I can do besides reboot it regularly?

There was a time where trying to work on server desktop was very slow and system memory usage was at 93%. With information from http://eightwone.com/2011/04/06/limiting-exchange-2010-sp1-database-cache/, set msExchESEParamCacheSizeMin to 16384 and msExchESEParamCacheSizeMax to 131072. After this, memory usage is lower and is currently at 68%.

There are no errors or warnings related to backup in Application or System logs.