LightningAC:
Could someone try to help me with this?
Yes. This entire board is full of people who enjoy doing just that.
You probably won't need my program because I am basing this off of the MultiStepper example of the AccelStepper library with the modified pinouts.
No. We do need to see your code. Even if I knew which example you modified, I would need your modifications.
Post your code. Use code tags. And you are right, this is likely a timing issue. I do not like pulsein for RC receiver decoding.