Sounds like the fluid level may be a little low.
I'd take it for a quick ride at least 3 miles, then park on a level surface, and check the fluid with the engine running.
It should be between the 2 "Hot" marks.
If it's not, then just adjust the fluid level as necessary to get it between those marks after a 3 mile road test.
Toyota transmissions are sensitive to the fluid level in my experience. Even over filling makes them do so weird things.
One time I over filled my Camry by a 1/4 quart, and it shifted very hard. I drained it, and filled it to the correct level, and it has been perfect ever since.
However I have noticed that on a cold start on a slight incline it takes it a second to engage into gear. (this only happens in drive. Reverse engages right away.) Like what you are describing. How many miles on your Tacoma ?
I just figured mine was doing this because it's getting old.
After all it does have 251k.