ford f250 s/d 7.3 psd electric problem

with engine running when there is a power draw of somekind (delay wipers, brake lights,ect.,)and even sometimes when you hit a bump in the road it affects the fuel shutoff, it's like you quickly turn key off and then back on. that seems to be the only thing that the problem effects. the more power you draw, the worse it becomes, when I hook up my camper with electric brakes the motor will die. checked a lot of things, running out of things to check, any suggestions, or maybe someone may know what it may be. Any help will be greatly appreciated. thanks!