Need 545RFE Help

Hi everyone! I really need some advice on my 04 Ram truck trans.
I was driving back from my aunt's house today and my transmission started acting up. The lockup would kick out on level roadway and then engage again. This would go on for a little bit and then it be fine for 50 miles, then act up again. This went on for 200 miles until I got home. The fluid level is fine but could stand to be changed, and no dash warning lights came on.
I hope someone point me in the right direction. I'm hopping it's something external and not the converter itself, but the way my luck is going right now.