Rajaruner

I have a 1993 Subaru Impreza WRX Estate 2l. This car was an automatic but has previously been changed to a manual. There are two faults with it and i was looking for some advice on what could be wrong. Firstly, there is a miss fire between 2000 and 2500 revs and the check engine light comes on too. Secondly when you are in fourth or fifth it makes a noise as if the gear box is going into overdrive or the clutch is slipping. An advice greatly appreciated.