Problem with rear traction

I've got a 99 XLT 4WD auto V6 3.0L, whenever I take off from a stop and the ground is wet (rain or puddle), my rear tires spin and I can't go for a few seconds. I also have a problem when I'm turning and hit a bump, the rear end wants to fishtail and I feel like I don't have much control. I've heard that it's a matter of the bed being to light, if that's the case how would I add permanent weight to the bed?

Yeah, that's the joy of pickups, having a light rear end. I cant think of any "permanent" solutions. In the winter I just throw three or four 70 lb sandbags in the back right above the wheel well area. other than that, I really cant think of any other solution.

check the tire tred also. ive heard of a person welding lead weights to the rear frame. dont know how practical that is or how it would effect gas milage. if you're accelerating hard: don't

you may also want to consider a rear locker for your differential if you dont have limited slip...like me..
although no LSD=LOTS OF FUN...keep that in mind