2001 F-150 Super Crew Transmission Problems

Hello. Hope someone can help? I have a one owner (me) 2001 Super Crew which seems to be having some overdrive issues. Under major/minor load, when the truck is in overdrive. Whether on the Interstate, State Routes or country roads. The transmission will jump, sputter, slip, etc. When you turn the overdrive off, it seems to stop this jumping. It seems as though the transmission is having a difficult time shifting out of overdrive to cover load that is being requested. In other words, it doesn't know whether to shift or not. Once the overdrive is turned off, the problem seems to be taken care of, although, I am starting to feel troubles even when the overdrive is off. I don't think this is an engine problem. The truck seems to run great and I have not had any "check engine" light come on. So, where do I begin? The truck has about 110,000 miles on it and is serviced regularly. This problem has become more noticeable in the last two months and has really gotten worse in the last week. Help me in the right direction if you can. Thanks in advance!