Mach3 CV Problem

Hi all,
Last week I updated from Mach2 to Mach3 the install was on a clean
windows , I placed the same machine parameters, I started a big G-code
file made by MasterCam to make a finish pase of a blow mold . Feed is
1000 milli-meter, the problem is that the machine movement is not
smooth at all , The 3 axis are hesitating (as if the CV option is off
and exact stop is on ),
the feed given by mach3 rapidly changing but not more than 450 !!
I have chaneged the look ahead parameter, CV feed and angle, little
diffrence but not good at all.
I went back to mach2 with the same G-code file , the movement is
perfectly smooth and feed is 1000 all long !

Where is the problem? Any Hints?

Thanks,
Shadi Salhab