Poor grip in wet conditions

Fishtailing comes from two things...First, all tires are not equal when on wet roads. There is a distinct difference between brands tires and even different tread patterns within the same manufacturer. To find the best tires for your vehicle, you need to experiment with different brands etc. (also look to see what other people are using and how well their vehicles handle.) Worn tires regardless of make will tend to loose traction as well.
Second, vehicle weight distribution (pertaining to weight actually pressing down on each individual wheel). Adding weight to the vehicle by loading up the back with heavy items sometimes helps but will destroy your rear suspension. I use a "non-traditional" fix for this by adding two 20lb flat lead weights to the rear axle (using two longer "u" bolts, one on each side, to fasten them under the spring, behind the brake assembly) With additional 20lbs at each rear wheel, the weight is not on the suspension but adds 40lbs to the rear axle weight, low, where it enhances traction and changes roll center in a good way You may also benefit by adding heaver sway bars to prevent "wheel lift" during cornering (both front & rear must be matched).
I don't know how aggressively you drive, but if you take it a bit easier on turns this will help as well. Driving in 4wd will obviously wear the 4x4 components faster than not using them, but using anything will eventually wear it out! (your vehicle would last a lot longer if you kept it in the garage and didn't drive it.) Use it when you need it...that's why you bought it! It dosen't rain every day!
Hope this helps you ...