The only router tool I've found that can sometimes stress a circuit is if TTCP is embedded within the IOS. (Most don't appear to have it.)
An easy way to stress a circuit is some type of external traffic generator. There are some free ones that will run on PCs that are often good enough.
Using one to generate traffic inbound from the Internet is often a problem unless you have access to another Internet connected site with more bandwidth capacity then the one you're testing.
Edison's suggestion of downloading large files is good. For best results, you often need to run multiple and concurrent downloads, also often from different sites.
