I have the 4 speed Auto gearbox and just wanted to check is 5th gear an overdrive so on the 5 speed box it would have a 6th gear as overdrive? If I go from 2nd to drive (which I assume then puts me to third?) then it will sit on about 3000rpm at just under 100k. and does not shift from there. When I turn on overdrive then it will drop down to 2200 rpm and take me to about 105/110 which I assume is 4th, and then if I back off the throttle slightly it shudders and seems to drop another gear, the rpm drops and its like it has entered a 5th gear? Running 33's BDG A/T. I read that the shudder might just be old/bad oil? have bought all new full synthetic oil to change it hope it helps.