I already published a question here earlier, with the symptoms of high rpm when stopping before complete stop. And high room when shifting from one gear to another(usually bit drops between shifts).
Recently I noticed that this happens only when shifting above 2500 rpm. So if the shifting happens before the rpm reaching 2500 it will be smooth and normal.
Replace the IAC valve. Cleaning will sometimes help but replacement is the best option.
Is this engine carburetored or fuel injected and if it has a carb are the secondaries vacuum operated or manual. If it has a carb it sounds like the secondaries are not closing fast enough. Matbe a dashpot adjustment if it has one.