when the truck gets warmed up,i tap the accelerator in drive or reverse and it starts hesitating and coughing and wants to stall.also taking off at low rpm I hear a knocking noise that sounds like it might be from around the torque converter(not completely sure about that) but quits when I throttle up.it runs perfect when its cold but starts after getting past normal operating temp.it also develops a vibration which sounds like a heat shield or something also only when in park or reverse.any ideas would be appreciated.