Well I've had my blazer for about a year now and ever since I've had it is has always done this.

Going down the freeway when truck is at normal temp it will kick out of overdrive if I let out of the gas a little, but as soon as I push back down on the gas it will go back in untill I let off again.

I can't seem to figure out what is is, can someone help me please? Thank you.

 

How are you determining that it is kicking out of overdrive?

 

Watching the rpm go from 2k up to 3k then back down. I can shift it into 3rd and the rpms only go up a little. I also have 2 codes coming up, 1 for evap emission control system vent circut, and 2 bank 1 sensor 3 o2. I don't know if either of these have anything to do with it but ill put it out there.

 

The RPMs raise up when you let off the pedal?

 

Yes, but not like normal downshifting. At time I can cruise 65-70mph and it will not go into overdrive untill I step on the gas a little harder then it will.

 

Almost sounds like it is your torque converter unlocking and then locking back up. You may have a bad torque converter...

 

Just to cover all bases is there any kind of sensor or andythinf els that could do this?

 

The TCC solenoid in the pan could have an affect on this, however, it should set a code.

You may want to consider getting it looked at by a few different transmission shops. With a scan tool, you can monitor the torque converter. Transmission shops should be able to do this as well as monitor other things pertinent (line pressure, etc) to the occurrence.

I say that the TC may be going out because it shouldn't allow that much of a rise in RPM.

Are your brake lights working properly? One thing just occurred to me. If the brake switch closes, it will cause the torque converter to unlock.

 

Would a actron scaner read this? I know they don't read codes for transmissions. Also where could I find pics of the tcc soleniod?

 

Probably not. You typically need a full feature scan tool would be able to monitor the transmission and the status of its various components.