I borrowed a 2003 Arctic Cat 400 fully automatic with fully independent suspension. I haven't ridin it on trails yet, just around the yard. I'll tell you what, this thing handles about as good as a slab of butter on a pile of hot broccoli. It is almost scary. Everything seems to be correctly adjusted on it but man o man, I am scared that once I get it on the trail, I am gonna flip it or something. Maybe it's the independent suspension. I have only ridden ATV's with solid rear axles. Is it me or does this quad suck at handling?

 

An independent rear suspension vehicle will have a better ride.

How deep are the lugs on the tires are they sinking into your wet grass? at low speed they can really grip.
Is it possible that there is some kind of pre existing suspension damage.
Look at the wheels from all angles in relation to the wheel wells and make sure the tires are sitting straight.
I bent a control arm 3 weeks ago and it made my vehicle almost imposible to ride.
Overall the machine should just be point and go. If it is that bad I would say you have a possible suspension/steering issue.
Talk to the person you borrowed it from.