Blazer wanders bad

[madman 72]

I drove my 75 blazer to work which is about 8 miles and I noticed that it wanders pretty bad. I had to be on the wheel ready for the next pull. I also noticed that it does it when i get of the gas, not even pushing the brake it puls and starts to wander. It has a 4 inch lift with addaleafs front and back and 35 inch big o tire mt's. on smooth roads it wanders alittle off and on and unperfect roads it is alittle worse. This cant be normal. WHat could be causing this. i am at a loss . Have any of you had this happen. How can I fix this? any help you all can give is greatly appreiciated thanks