Tektronix TDS3000 series max trigger rate
The problem is the scope has 10kpts which means every time it is triggered, it must take 10kpts and then the software must transfer those points out of the scope. 

The max trigger time is related to how many points your acquiring, my suggestion would be to use a fast acquisition mode if you have one on your scope (1000 pts). 

Another problem is if I'm not mistaken, pyvisa is polling to get the information back from the scope, if the information gets overwritten before the computer can get the trigger, then you won't see it. Part of the problem is PC's aren't meant to do real time operations and do things in the ms range. 

I did make measurements with a slightly better scope and matlab visa for making measurements of USB packets, I was getting roughly 5 second with a fast acquisition mode. I couldn't see all the packets, but I had enough information to find what I needed to find.