Bought a used 2000 civic with 178k automatic, gears a little sticky when shifting would it cause problems to flush all the fluid out and refill with new or better to do it little by little? Thanks

 

Problems? No. If the transmission has issues, a fluid change will not solve them, only delay them.

To determine what is or is not a problem, you need to provide more information. "sticky" is not a technical term, and as such must be defined by you.

When I think of sticky, I think of too much honey on my toast.....

 

What is the condition of the current trans fluid?