We have begun to experience some strange, intermittent episodes of reluctance to move up the gears whilst accelerating in our 2010 Subaru Forester XS automatic (bought new and approaching its dealer 48,000 mile service and transmission fluid change).

It dawdles and dithers for a bit and can then take off like a WRX at the start of a rally stage! The problem is worse when cold. Consequently, smooth progress is difficult; accelerator on and off as one tries to drive with some decorum. Engine seems fine, rather the transmission at fault. Any idea?