2001 Jeep Wrangler that hates highways

I have a 2001 Jeep Wranger (4cl) automatic that has hated highways. When i drive on the highway, after about 4 hrs, my jeep decides to slip into neutral. So i initially have to hit the gas pedal to make it down shift and then it seems okay but of course after about an hour it does the same thing. Hence a long ride becomes much longer. I usually pull off and let it the engine cool down and that seems to help and i can resume the highway once again. I have had the transmission looked at and a transmission flush done. I have been told that i do not need a transmission but the mechanic has no idea why this occurs. Any help would be most welcomed. thank you!

If your mechanic is not a transmission specialist then - no offense to him/her - but s/he is probably not qualified to make any sound judgments about it. You need to find your most reputable, local, independent transmission shop & have them look at it.

Has the check engine light come on? Regardless of that, has the computer been scanned for error codes? If so, what were they.

Was the pan dropped and the filter changed when the transmission was flushed? Was the transmission cooler flushed and blown out separately when the transmission was flushed? I would also recommend having an independent transmission specialist check it out. The pump on Mopar transmissions have often failed from apparent foaming of fluid due to restricted coolers or cavitation from restricted filters. But I am not a transmission expert. I just serviced them and replaced them.

Thank you both for your feedback. I am setting up an appt with a transmission specialist to see what the problem may be. The transmission cooler was flushed, the pan was dropped and the filter changed. This was done because i specifically asked for this to be done. I am not certain to it being blown out separately. The check engine light has not come on and i have had the computer scanned for codes. However there were no error codes.
Thank you again to both of you for your comments.