Do you have on-demand (read) AV running?
Whenever a large file is opened by an application, the AV scanner is going to scan it, and hen AV is running it will usually take up nigh-on 100% of CPU time, so everything else - including TM - just has to wait.
I found that java
was causing this on my system, so I added the java .exe's (large files) to the exclusions list and it improved the situation considerably.
A lot of websites seem to feel the need to execute jscript (java) for no reason other than to look cool. Hence why it can affect your browsing.
SD