I had this problem after installing the game on my (fairly new) pc even with the patch, but I found this handy solution on gamefaqs forums (here
Posted 12/17/2010 10:35:53 PM
I have found the solution to the slow motion problem. Simply right-click your SWTFU2 desktop shortcut, click properties, and in the "Target" box (the one with the path and SWTFU2.EXE add "-variableTimesteps" (without the quotes) after the original text. Make sure there is an empty space between the path in the quotes and the text you have entered. This should solve your slow-motion problems forever.
I am playing TFU2 on a Pentium D Presler 915 overclocked from 2.8 GHz to 3.73 GHz, so I have had my share of slow motion, as the CPu is below minimum. With this fix, there is some framerate drop, but the slow motion is gone.
Note: I haven't tried this out, but I'm also using the "-performanceThrottling" switch in the shortcut. If the above solution does not work on its own, try adding this too in the same manner.
The solution in bold worked wonders for me, even with the 60 FPS unlocker. Now I can play the game with all the graphics features turned up and it runs like a dream.