you drain it if a 3/8mm rat bolt on the bottom of the gearbox the you level the car and then you tight up that bolt then you undo the 17mm bolt just above the other bolt and then you fill it until it...
you have a clutch problem. but first try and use a thinner oil like mobil1 5-50 as long as you don't have lsd then it's ok,but if you do have lsd then you should us red line(top of the shelf gear oil)
get your injectors cleaned under ultrasonic. but if you have a 2 1/2 inch exhaust then it is too big anyways, reduce it to 2 to 2 1/4 inch and you will get more economy and performance.