Jeep gets stuck in gear & rev's high on hwy, everyday

What is your question?

for the last 6 mnths or so; everytime i drive my jeep on the hwy, after about 1/2 hr or 20-30 miles, it's jumps in rpm for a sec, then stays in what seems to be 3rd gear, until i can get off the hwy & park it for about 10 mins, before getting to my work or home. we are a 4 jeep family & i love my '03 very much & NEED help w/ this. i've taken it to two mechanics & dropped almost $3k & its still doing it, really dont want to get rid of my jeep, getting desperate for an answer......thnx u guys