transmision shifting at high rpms ???

I have a check engine light and my x-mision shifts at high rpms,( like 2000 and it doesnt want to shift into 3rd or overdrive ) the motor is running smooth, I was working on my lower fanshroud , it rubs against the fan every once in a while...had the skid plate off....I was also trying to get my transfer case fluid level check bolt off, it was running fine before I was doing the previous stated work, Ive looked all over for a bad conection or vacume leak,,,didnt see anything out of the ordinary...but im sure its something Ive done .....any ideas? is there a control module or something that controls shifting in relation to the rpms?

Thanks in advance for any ideas....

This may not be your problem, but I had a bad O2 sensor causing my trans to not shift. It was just revvving and not shifting. I unplugged my O2 sensor and took it for a drive and it shifted fine. Drove to the dealer with it unplugged and got a new O2 sensor. Drove home, put it in and the problem was fixed. My buddy at the dealer said the bad O2 sensor is on the same circuit as the trans shift cylinoids and it must have caused them to get tripped. Hope your prob is as easy a fix.

Ok ..I dont know how I did it ...but I did it.....The mass air flow sensor was hooked up backwards....everything is good again