Engine revving in first gear when cold

My truck is not engaging into gear on the Initial press of the throttle when engine is cold (in drive, moving forward). It will rev and fall, then engage on its own.

this only happens on the initial press of the throttle after engaging into drive. After the truck has sat for a while.

It engages into reverse perfectly fine.

Is this a characteristic of the truck? Or is it something I should have looked at?

the truck engages and runs perfectly fine after the initial take off. Trans shifts good.

 

Throttle could be sticking a bit due to carbon and downtime between drives. I'd start with cleaning it.