Sticky 5 to 4 shift

[FPerron]

This happens only at high speed (120 - 135) at the end of a long straight (like at Watkins Glen) when braking hard (double clutching, heel and toe, of course). It feels like the shifter is getting hung up in the gate between 5th and 2nd. I have no problem with the 4 to 3 or 3 to 2 shift. Although it feels like the transmission is torquing around and making the shifting imprecise, I've got the STI trans mount, a factory short throw shifter and Kartboy front and rear shifter bushings. Anyone else ever experienced this? It's certainly distracting when trying to slow down from such a high speed. One other thing, during maximum deceleration, I'm right on the ABS (running Toyo RA1s).