2001 Nissan Maxima Nobody can figure out what is wrong!

After I drive my car on a highway for an extended period of time (couple hours) and get off onto a street, after about 10 minutes my car will not get into gear. So, after I get off the highway and I am driving around 40mph I come to a stop sign. When I go to accelerate the RPM's shoot up and the car won't go over 20mph. The transmission won't shift into gear. The first time it happened I pulled over and waited about 5 min when I decided to try it again the car ran perfect. It happens every time. Now I can fix it right away by slowing down to 15 mph putting the car in drive 1 then drive 2 and finally drive. I have taken it to 2 different places and both of them have not been able to find out what is wrong. They have told me everything looks good (no codes, fluid, filters. Etc.) Any ideas? Please help! Thank you so much for your time!