transmission shifting problem only on 4th and 5th gear
 

only on 4th /5th gear on drive , when the car shifts from 4th to 5th gear rpm goes from 2000rpm then suddenly jumps to 5th gear and the rpm goes to about 2500rpm , shifts to 5th gear then rpm drops back to 2000 rpm. is my transmission going bad??

Not necessarily. Mine did that very thing occasionally and it was determined to have a sticky valve. A full transmission service (at a Porsche dedicated shop with the proper fluid) seems to have solved the problem.