If that trans is all factory, and I mean it's not been rebuilt, the prior owner could have been running a different type of fluid in it, and if so, that could make it hard to get in gear. I would drain it, and check for fine metallic particles, and run fresh fluid through it getting out as much of it as possible. Then put new fluid back in it. Ford calls for strictly "Mercon" for the t45. There was a TSB by ford for the t45 to use Mercon 5 where regu5 Mercon was used. Me personally use regular Mercon, and she shifts flawlessly. I actually use the "Castrol Dextron/Mercon" its a black quart bottle. Try to change it and see how it does. Some other fluids can make a tranny be notchy as can be. Good luck!