my 94 honda civic lx sometimes wont reverse

Make sure that the fluid level is full. If the level is full, take it to a transmission shop for diagnosis. Have you ever changed the fluid or filter?

no I havent got the transmission fluid done yet but also when I drive it on d4 I cant go over 40 mph it start stalling and so I have to drive it on d3

do u think its cus of my filter or do is my transmission going bad

Is the "Check Engine" light on?

yes

Get the engine codes read and correct the problem. The engine problem might be causing the transmission problems.

what do you mean

Go to the auto parts store and tell them that you have a check engine light. They will plug a scanner into your car and tell you what is wrong. It's usually a free service at the national parts store chains.