How long is a minute in FSX?

Has anybody else experienced time compression. I have found that most of the time 70 or so 'sim seconds' elapse in a real minute. This is sometimes obvious as the second hand on a clock gauge rotates at differing rates. Occasionally 1 minute = 60 seconds.
The sim seems to jump as the time lurches forward.
I run Ultimate Traffic at full pelt, and this seems to exacerbate the issue - seems odd - however removing this does not return time to normal.
I am running AMD 3800+ on a M2N SLI deluxe mobo, ASUS 6600XT Video card 256Mb, and 2GB DDR2 @ 667Mhz.
I initially thought my overclocking of the CPU from 2GHz to 3GHz may have been the cause (although system clock perfect), but all oc changes have now been removed.

Any thoughts from anybody would be welcomed 😕

Chas