This occured the first time the other day at a stop sign. I came to a stop then pressed the gas and at first the car revved up to 3,000 rpms before drive engaged. The other day I came to a complete stop and upon pressing the gas I was unable to go forward, only reverse worked. I shut the car off for about 10-15 minutes and upon turning it on and revving it up was able to engage a gear. I have checked the tranmission fluid level as well as the gear box fluid level and both are full. Is there something else it could be that I could check myself or replace?