I had an issue that sounds slightly similar. My car would drive perfectly fine when I first started it and drove around for a few minutes. Then after the engine warmed up, I would try to accelerate and the rpms would go up, but the car wouldn't accelerate. Even from a stop at a light, I would try to accelerate and the car would just sit there basically. I thought it was a transmission issue, but it ended up being a problem with my air intake. Fixed the intake, fixed the problem. Good luck with yours, I hope it's something as simple as mine.