So when did you notice this ? Was it fine for 2 years ?
Are your tires bald now ? Do you have the original tires ?
Without seeing your truck i'd say you are hydroplaning or your tires are junk. Broken rear springs will do the same thing. DO NOT put sand bags in the back of the truck. FIX
the problem. I don't know what your insurance company says
but ours says that a sand bag or cement block is a moving
projectial. The extra weight could and will move into the
cab upon a sudden stop and the moving projectile could and might enter the cab of the truck and kill or cripple you.
If there is a sand bag or cement block found in a truck in
an accident in our city you have no coverage. The thing is why does this happen now and not happen 2 years ago ? Did
you never drive it in the rain until now ? What happend
from the time you bought it until now ? Why did you not notice this 2 years ago when you first owned your truck ?
What did you do that is now different ?

It has been doing this for the whole time I have owned it. The tires that are on it are Coopers and they were on it when I bought it. The tread and air pressure are good. I will stop today at my mechanic and ask him about the springs and get his opinion on the tires. Maybe they are junk and I need new ones.
I never thought about the sandbags as being projectiles. Thanks for that advice. I take such care to tie everything down when I use the truck to haul anything, but I didn't think about the sandbags that way.
I'll let you know what my mechanic says. Thanks again!
Julie

Pretty common condition for a pickup. Adding wieght to the back is a common practice in winter months. I don't think it's any more hazardous than hauling anything else which is what the pickup box is for.

Our '98 Dodge Durango did the same thing with the original Goodyear Wrangler tires. Problem went away when we bought a set of Bridgestone tires. They're not lasting as long as the goodyears did, and they've gotten noisy as they wore. Still no more one wheel burn outs on wet pavement though.

Before switching tires I was considering adding a positrac unit to the differential. Seems like the parts would have cost me around $350 which wouldn't be bad since I can do the work myself. If you were to pay a shop it would probably cost around a grand.

There's a couple ideas for you.

Pickup trucks are noted for being light at the rear when empty. Intesd of a weight ratio of 60% front and 40% rear for a rear wheel drive sedans, it more like 70% front and 30% rear. Couple that with a good engine up front, and likely a more agressive rear drive gear ratio, maybe over 3:1, you can easily spin the rear tires especially when turning fast enough to remove most of the weight on the inside rear wheel. On wet pavement, it is spin city when those wheels go over a paint stripe.

I stopped at my mechanic today and he said the springs aren't the problem, it's just too light in the rear. I have the extended cab, but I also have the full length bed with nothing in it. He said before I try the sandbags, bring the tire pressure down to 25. If that doesn't work, try the sandbags.
I live in Florida, so snow and ice aren't the problem, but those sudden showers are. My Camaro Z28 had more traction in the snow than this truck does in a drizzle!lol Also, it's legal here to put people in the back of a pickup, so I think the sandbags will be ok, but I won't try the cement blocks. I looked up reviews on this model and there's a lot of people that say it's a bad fishtailer in the rain. Plus, it's a "girl" truck! I keep the bed clean, no toolbox or junk in it to weigh it down!lol I bought it because the height of the seats is great for getting in and out of with my bad back. Also great for plant shopping.
Gary, the Dodge Durango is the Dakota with a cover to it, so you know what I mean. It has good Cooper tires on it and I read of one guy who tried 3 different brands and it still fishtailed.
Thanks for all your help. I'll let you know how the tire pressure thing works. At least we're going into the dry season here.
Julie