You need to give more info to get more than a flippant answer.
What codes, if any, are present? A more expensive scanner will also pull codes that don't trip a CEL, but you probably have a check engine light, no?
What else is it doing besides stuck in 5th gear? Can it go in reverse, park, neutral? Does the engine idle/rev fine? Does it shift into any gear normally or hard?
My '06 Altima got stuck in 5th twice. Once for a crank position sensor and then again for the front cam sensor. A friend's Maxima did the same for the rear cam sensor.
Pull the codes and research what those codes mean. You can throw a lot of money at your car and still not fix the problem if you're just replacing parts that you have a hunch about.