transmission slip

Can anyone tell me how to stop the grinding sound when shifting into reverse on an Alpha 1 outdrive? It also feels like the reverse is not engaging unless I push the shifter down a little farther, could this just be an adjustment in my shifting cables? This only happens on the Port outdrive, the...

I have twin 4.3 mercruisers, yesterday i was at apporximately 3000 rpm and the starboard engine tranny seamed to slip, when I brought the rpms down a little I felt it engage again. Could this be checked while in the water? I cannot trailer it. Could it be something simple? can I still use it...