My 1993 SR5 will not go into overdrive unless I manually do it at the gear shift

What is your question?

I have been having an issue with my t100 not wanting to go into overdrive when regular driving or trying to pass into another lane. I can activate the overdrive manually at the gear shift with a press of a button but cannot activate it when pressing the gas petal to gain speed on hills and pulling my boat. Any clues on why? Thanks