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.