Overheating during winterization

'03 BU VLX with monsoon. I had it in the water about a month ago w/ no problems. I replaced the impeller at my last oil change about 3 months ago. I went to run it for winterization using my fake-a-lake which I've done several times and noticed that water was trickling out the exhaust like a drop at a time. After about 10 minutes of watching the temp gauge it started running hot @ 180ish. I removed the fake-a-lake and checked some hoses, boat intake to vdrive, vdrive to water pump, both had water in them.. I put the garden hose into the water pump in hose and it just wasnt sucking it up (or hardly...). My previous impeller lasted for 3 years and when I yanked it, it still looked good. So I have a hard time thinking it's the impeller. I don't really know how the thermostat works in this situation, but maybe it's not working?? Any ideas what this could be? I leave for a business trip in a couple days and will have 3 nights 32 and below consecutively, so at this point I'll drain the block and disconnect the exhaust manifold hose and hope for the best. Just starting to get really worried and I don't have a chance to take it into the shop between now and then.

Similar thing happened to me a few weeks ago, impeller was shot, nothing left, and it was blocking any water from going through....
Something clogging the lines maybe, or Like you said the thermostat, but no knowledge on that.

I checked the impeller, it looks good. I checked the transmission cooler and there was a piece of plastic (like hard candy wrapper) in there. So the thought was it was blocking the water from cooling the engine. Tried running it again and I saw a trickle coming from both exhausts. I shut it off after it was 165 degrees. How do I know if it's working or not? I think it was going to overheat and didn't want it to run, but not 100% sure. My friends nautique gushes out water of it's single exhaust, but I had a trickle from both and it looked like it was taking in very little water from the garden hose.

It could be your circulating pump.
Pull the belt off, and spin the pulley on the pump. If you don't feel any resistance, or it wiggles, or you hear bearing noise, the pump is shot. About a $100.00 part on a Merc. Black Scorpion, not sure on a Monsoon, but shouldn't be much more than that.