So I have an R50 with a 5 speed manual that had a new tranny, clutch, and flywheel put in about 6000 miles ago. The car has 99k miles on it now. I first noticed this problem at about 98k. Basically, my transmission falls out of second gear through a tight S turn at my local track. I don't know if it does this in other gears. The odd thing is that it only happens when I have a passenger, and very rarely when It's just me in the car. The extra weight seems to be a factor in whether or not it will slip. The gear slip can be prevented by holding the gear **** back while going through the corner. This leads me to believe it's an engine mount issue, an issue with the linkage, or something to do with frame stiffness. Any input? Most people I've talked to haven't had engine mount problems, so my mechanic may have just done a shoddy job putting everything back together. (He also forgot to put a few bolts back in place on the crash tubes and the bumper.)

For the record, the transmission does not slip during straight line acceleration no matter how hard I push the car. I am extremely doubtful that it's the transmission itself unless the design is just weak overall and is not built for such tolerances. The car really is on the edge through that turn with tires squealing.