I was told to put the entire contents of those very small plastic bottles of injector cleaner into full tank of fuel, it was better after running in 5th gear at over 50 mph it got even better after some redx lead replacement, same type of bottle size...and even better after I changed the air filter, an easy cheap do it yourself job....I live in a country area in England where the car has to pull straight out and up a hill after going around a roundabout...total outlay £20
give ti a go , it can't harm the vehicle, and prob. needs doing anyway...esp. the air filter.

If there are no lights or ECU codes, esp the water temp sensor, then the usual remedies are to use injector cleaner, and clean the throttle body, check for water in the fuel filter (and the fuel tank). Make sure the engine oil level is full, and so on. I assume a hill outside Sydney doesn't get enough altitude to be an issue, unlike a hill outside of say Denver, CO that goes up near 10,000ft above sea level where you should expect a significant power loss.