I have an Art Carr C4 with a reverse manual valve body. Mine will rev some on the 2-3 shift if my shifter linkage isn't adjusted just right. I have to make sure third gear on the shifter is clearly all the way into the detent on the transmission. Otherwise it seems that second disengages a split second too soon or third engages a split second too late which causes the rev. Mine still grabs hard when it hits so I'm pretty sure my 3rd gear clutches are ok.
You can see my 65 fastback at: http://hottarod.stangnet.com/
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You can see my 65 fastback at: http://hottarod.stangnet.com/
http://members.aol.com/macstang/Gifs/macstang3.jpg