Automatic 4l60e Trans won’t shift into Overdrive

Have a 1997 Chevy K1500 pickup with a tad over 300k miles and now the transmission won’t shift out of third gear into fourth (Overdrive).  The fluid is still red and doesn’t smell burnt.

I’m not sure the direction to go on a budget. My assumption is the transmission is bad and so checking online I can pickup a used transmission in unknown condition for around $400-$700.

Now from doing online research I am learning it could be…

Torque Converter

The loss of overdrive could be when the torque converter fails to lock up.  When the torque converter doesn’t lock the vehicle will travel at a higher rpm down the highway.  The whole point of the locking converter is that it is supposed to create a direct 1:1 connection between engine and transmission.

A good way to tell if this is the case is to look at the vehicles RPM on the highway.  If the needle moves up and down with the most minor of rpm input change, than it is likely that the locking mechanism has failed.  It feels so different going down the highway that it can be confused for a lack of overdrive.

Band Failure

Most of the time the overdrive gear is going to fail to engage due to the wearing of the band for the Overdrive.  The servo will no longer be able to engage it because of this wear.  This is the physical problems that stops overdrive most of the time if no other issue is detected.

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  1. Had the same issue not able able to shift out of 3rd to 4th (Overdrive) so I drained and dropped the transmission pan and when I saw all the metal shavings in the bottom of the pan it told me its more serious than a solenoid. So searching for a used transmission (4L60e) for 96 and 97 GM truck for a four wheel drive truck. These people are crazy asking $500 or more for a transmission that has over 250k miles. Thats basically just buying a core.