Transmission slipping?

I think my transmission may be slipping because when I throttle down (like pulling up a rider) it's like it goes out of gear (neutral) has a spinning sound and then catches back up and goes on as normal. It has gotten a little worse over time. It is much worse when just starting out (cold engine). After it warms us a bit, it doesn't do it much, if at all. It also shuts off sometimes when idling slowly back to pick up a rider. I initially thought it may have something to do with the fuel filter. Anyone know what may be wrong? I'm going to take it to get it serviced pretty soon and just wanted to know what kind of cost I'm in for. Thanks. By the way it is a 350 Mercruiser.

Have you checked the transmission fluid level, may just be low? Inspect the fluid for color and smell, should be pink, not brownish or milky and should not smell burnt. Has it been serviced regularly, every 100 hrs or once a season?

check tranny fluid like tigemike stated. trans fluid is used to create the pressure that holds it in gear (clutch plates together), if it gets low it will come out of gear.

Thanks guys, I'll check that this afternoon. I don't know why I haven't done that yet.

Any ideas on what may be causing it to go dead when going idle speed?

"Any ideas on what may be causing it to go dead when going idle speed?"

Sticking IAC (Idle Air Control) motor. Typically, it can be removed, cleaned with carb cleaner, and reinstalled.

Mine did the same thing, checked the fluid level and it needed some. Now the fluid turns milky so there is water in it.

Now when the boat is on and in neutral it is still moving slightly forward (won't come completely out of gear i guess). Is this a clutch going bad? I'm pumping all the fluid out tonight to see if a new batch will get water in it.

A-dub. You will have to fill, run, drain/suck, the transmission repeatedly to get all the water out. I got water in mine and think it took 6 drains/fills until the fluid did not look like a strawberry/orange milkshake.

a-dub, it may also have warped the clutch plates. when it slips like that, they heat up quick and the plates are not thick at all. if it creeps in neutral, that is usually what happens. to the op, do not keep running it like that because the transmission slipping will lead to those warped clutch plates. turns a fluid change into much more. is it dd, or vdrive because i know a lot of tranny issues in dd are from alignment issues. just rebuilt mine in july.

also if it is water, check the tranny cooler. that is usually the source and they aren't too expensive.

Thanks Ryan and bmartin. It is direct drive. I'll have to have the alignment and prop checked. Thanks!