The Overdrive will not engage sometime?

If you're lucky, there's a shifter problem that's causing the transmission to not shift into high (overdrive) gear. If you're not lucky, it's an internal transmission problem. I assume that you've checked the trans fluid and it's OK. You need to find a transmission shop or a Lexus/Toyota specialist for a diagnosis. If you want to find a Lexus specialist, here's our directory link for you: https://repairpal.com/lexus-repair-in-crestview-florida