hey im having trouble with my dads ram 1500.....it has the **** that selects 2wd 4hi or 4 lo

okay heres the problem in 2wd it makes a horrible noise and jolts the truck about at speed.....so switch it into 4hi and the noise and vibration and jolting stops.......but now i have another set of problems it makes a weird clicking noise at low speed when backing up and trurning, turning is more difficult in tight spaces in 4hi, and its still not a true 4wd because its sending all the power ot the rear wheels still...can anyone think of what could be causing this...please i need some help