Hello guys I'm sorry for my bad English first, I'm from quebec ( yes I'm a ****ing Frenchfries) so English is not my first languages... by the way I hope you guys can help me. I have a 99 blazer 4x4 4 door and recently I feel a bad vibration on the truck (under the truck ) but just when I accelerate, no matter if I turn or go straight or if I'm on 4x4 or not, no difference. It's worst when I accelerate from a stop and I don't feel anything on the highway. My ujoint looks tight, drive shaft look good so i don't know what is the problems, anyone know?

 

It sounds like a u-joint to me. Make sure the vehicle is in neutral when you check them so they have no load on them. Try to move them in all directions. There should be no detectable play in the joints.