Engine stumbling and dropping oil pressure..

if it takes 30 minutes to act up, i agree it is most likely heat related, you may want to check your fuel line, possibly try to protect it from the heat, i have had ignition parts that were heat sensitive also, if you have new headers ,they will really put some heat into the engine bay, do you have a temp guage ? if so what is the motor running at after that long? is the engine bay getting hotter than normal?