00 malibu problems

my friend has a 00 malibu v-6 and it has a missfire somewhere in the engine, it almost sounds like one cylinder isn't firing. i checked the coil packs, their ok. he said he replaced the plugs a while back but it is a recent problem. i hooked up my scanner and the only code was something about oil pressure. in the history it did say #6 has misfired twice but is not currently doing so.

also when i hooked up my scanner i found his trans does not recognise what gear he is in. the PRNDL data only said "??????".
any ideas?