2002 Other Jeep Models High Idle

I have a jeep grand cherokee laredo and it has a high idle problem. When I start the car it idles at over 2000 rpm in any weather type. When I shift it into gear it proceeds to go down. When i am driving down the road at any speed but more so the higher speeds betwee 60-70 it tends to rev up. The check engine light will then come on. After a few days it will stop doing this and the check engine light goes off itself. Then it will happen again a few days later, I notice it doing this on longer trips rather than just in town driving. I noticed that since it has been doing this the vehicle will not want to shift twice while I am driving. I will drive at 65 mph with the RPM's up to 3000 and have to slow down to 55 before it will shift finally and I can drive at full speed. please help!