This is a 1991 Ford Mustang with a 2.3 liter four cylinder engine. The automatic transmission is slipping when it’s shifting to higher gears. The first thing to check for is a leaking line which could suck air. The next thing to do when your transmission is slipping is to remove the transmission pan. When the pan is removed a couple things can be done. First the arrow points to the magnet that will pick up some of the worn material. There should be a minimal amount of material on it, if not there may be larger problems. Also this is the time to replace the transmission filter which may cause slipping also. This transmission needs to be rebuilt as it has worn clutches that need to be replaced. Most automatic transmissions are built very similar.