I have a 2000 bravada and it will shift out of overdrive when doing highway speeds after driving it for around 30 min or so. First I will notice the torque converter disengaging and re-engaging and then shortly after it will jump into 3rd. Not towing anything with the vehicle. Just jumps out of overdrive. Replaced the TPS and the MAP sensor as well as the MAF. Had just about every electrical component replaced in the tranny including the wiring harness and was told the tranny is mechanically sound. Tested the PCM and it'* normal too. No codes at all except misreadings for EVAP, EGR, CAT, and HTR. Any help would be appreciated!! I'm at my wit'* end!!

Have you replaced the ignition switch recently? Ever?

GM pickups, */10'* Blazers etc all had ignition switch issues.

No I haven't. Would the ignition switch actually affect that?

Yes, because of the high amperage load going across the contacts, the contacts don't pass enough current.

https://blazerforum.com/forum/articl...-switch-33465/

I had pretty much the same issue with my Blazer too.

Ok well I'll try anything at this point. I've practically replaced everything else down to the engine block itself lol. Is the ignition switch something I'd be able to do myself? I don't have much knowledge with the electrical portion.

It'* fairly easy to do. Remember, if you do this yourself, make sure you order a ignition electrical switch and not the ignition key lock.

I will definitely make sure it'* the ignition switch. I'll keep things posted on if it fixes it or not. Thanks for the help!!

Yes, please keep us posted.

Check if there is P1870 fault code set in history. Excessive TCC slip can set this and inhibit 4th gear and TCC apply. Will usually happen when hot. If you have a ignition switch issue you will have reverse and 3rd gear only(also a 3rd gear start) due to the loss of amperage on the pink wire to trans connector terminal E from the ignition switch. This circuit provides power to all the solenoids in side the trans. With no power both shift solenoids are off providing 3rd gear. Both shift solenoids are on for 1st gear,Solenoid A is turned off for 2nd, and both are off for 3rd. If you still have 1-3rd gears when the problem is active it is possible there is another issue. Have had these with wear in the tcc apply valve in the valve body causing TCC slip. Also when the code sets it will usually get a firm shift as it defaults to hi line pressure and won't always turn on the Check Engine Light. Hope this is helpful

Depending on whether or not the ignition switch fixes it . . . I'm curious who told you this.

I'm also curious how many miles are on it.