2005 Ford F-250 RPMs drop to 250 under braking, almost stall

I have a 2005 Ford F-250 super duty/5.4L gas/auto(trans.)/2-wheel drive/125,000 miles. The problem i'm having is when i'm driving(in drive) everything is fine, rpms are fine, runs smooth, everythings good but, when I brake coming to a stop the rpms drop down to around 250 rpms and it acts like it wants to die(stall) but, it doesn't. Then when I come to a complete stop the rpms will come back up, everythings fine, idol's good. Also, when I back up( in reverse) and cut(Turn) the wheels hard, it dies(stall). In the last couple of days however, when i'm at a stop(in drive) and cut the wheel hard it will die(stall) sometimes not always and just started doing that in drive. Can anyone help?Thanks, guys.