when the jeep warms up the transmission wont shift out of second is an automatic.had solenoid packs replaced and no mechanic has an idea.external cooler has been mentioned along with replacing pcm.any help would be great.

You need a transmission specialist. You general mechanic and the dealer typically are not it. Dealers send out for transmission work more complicated than fluid changes.

More likely an internal transmission problem. Replacing the PCM will do no good. The TCM controls the shift points. Any problem with the TCM will have trouble codes set. This should turn on the Check Engine light.

The external oil cooler has nothing to do with it unless it is leaking.

Your transmission is going into ‘limp home’ mode, which will limit it to 2nd gear. There are any number of reasons why this can happen, from a failing speed sensor to a serious internal problem. The only way to know is to get the transmission’s trouble codes read by someone that has a scan tool that’s up to the task.

I’d avoid shops like AAMCO and Cottman like the plague–they will insist you need a rebuild regardless of what’s really wrong.