It's a diagnostic move.:D
If in case for some reason you are not getting a correct reading on your fluid and it's sucking air.
One quart of fluid could solve the problem, or tell you the trans needs to come out.
I'll tell ya though, reverse is usually the first to go if it's low fluid because reverse uses more fluid to apply than the other gears.
You said reverse is fine, so it leads me to believe the level is probably ok or close enough.
The extra quart is still worth a try, as you don't have much to loose at this point unless you just want to tear it apart for the fun of it.:D
