I have a 99 blazer 4wd auto rhd 4 door, in 2 hi everything is fine, in 4 hi under acceleration it pulls hard to the right, needs about 1/4 turn on the wheel to keep it in a straight line, 4 low bangs into gear and shifts randomly, i know the people who owned it before me never used 4wd (bought it off my boss and i know he wouldnt bull**** me) but no idea before that as he is the first owner in australia, i was told to check out the front drive shafts for the 4 hi problem but the 4 lo problem seems much more serious, any one have an idea what it might be and what is needed to fix it?

 

I would check the front suspension. Look at the wear patterns on both tires and make sure they are uniform. In 4wd you are applying power to the front wheels which puts more load on the suspension up front. In 2wd, you are not applying the same load to the front. I would start with checking the tie rods, idler, then control arm bushings and possibly ball joints. My guess would be the idler arm as it might be flexing under a load. You might also jack up the front end and roll the wheels to make sure nothing is binding.