I have a 2005 Saab 9-2x Aero (WRX) 141,000 miles, completely stock, with the 4EAT automatic. Under full throttle, at about 70 mph, it will shift from 3rd to neutral (and redline) rather than shift to 4th. I must let off the throttle and give it a few seconds to find 4th gear when this happens. Under normal acceleration, it has no problem going from 3rd to 4th gear.
I have just replaced the transmission fluid and filter (using genuine Subaru stuff) and still the problem persists.
I have never driven anything with an automatic transmission before and really don't know where to start with this, it is also difficult for me to find anything on the web about this exact problem, so any help would be appreciated. Thank you!