au1 xr8:help

[x_RYD_x]

hey peeps

im having a problem with my au1 xr8.. basically as follows

ive had my transmission rebuilt and for some reason it will randomly drop into 3rd gear then back into 4th then back to 3rd ect ect but only when the speedo shows 70-80km/h now i did have 3.9's fitted awhile ago before the trans rebuild and it didnt do this, i havnt had my speedo corrected, now i cant see how it would be because of the ratio change because as i said it didnt do it before the trans rebuild.. any ideas as to what this could be guys?? oh and the car was xcal 3 custom tuned at the same time as the trans rebuild and the tuner said because of my pcm he couldnt change the axle ratio .

[millzy555]

U sure its not the torque converter locking up?, 80km/h sounds spot on