Spring RTS Engine

I have been using spring an older version (0.75b), and it works fine with high frame rates and good graphics. when i switiched to the new version, i have had problems. first, the game slows down every 5 - 10 minutes to 1- 5 fps. this is from a normal value of 60- 70 fps. Also, the cpu usage jumps erratically. from a normal of 7-11% to 55-70%.

My computer is:
Intel Dual-Core 2.5ghz
Nvidia Geforce 8400gs (512 mb Vram)
4 Gb Ram

I run the game on medium/low
I am using complete Anhilation

This may or may not help, but try disabling antivirus software while playing, sometimes that causes slowdowns.
Also, disable threaded optimization in nvidia control panel for spring.exe.