Can I tow a small fiberglass boat with my Park Ave, it weighs about 2000 pounds

How many miles do you have on it? And how far do you plan on towing it? I'd imagine if your tranny has been flushed recently and has a cooler (an Ultra would have one stock...) I think it would be fine, but I've never had any experiences...

and you might wanna give us some info, like what trim level, year, mileage etc...

about 100k, trany fluid and filter chgd regular. I would think if I dont tow in overdrive I should be ok. How much are they rated to tow ?

oh and its a 1999 Park Ave NOT Ultra model though. 100k miles

Not sure if they ARE rated to tow, just make sure you tow out of overdrive and try to avoid hilly roads...

I do tow a small popup camper with my '98 LeSabre; but I would not tow more than 1000 to 1200 lbs with an H-body, no matter what suspension and support mods (tranny cooler, etc.) it had.

2000lbs might stress your trans too much..a LARGE cooler would be really nice to see.
Short of that..one shouldn't necessarily consider getting up and going with the boat..its..stopping with stock sized brakes on your Park Ave..not there there is larger brakes or 4 piston calipers available..but you wanna make sure she can stop in a hurry if needed...

I agree with the posts above. I mean, 2k is just way too heavy, especially when you consider the trailer is probably another 300-500lbs (I think, bad estimator). Do yourself a favor and borrow a friend'* truck or something. Or a rental