Hello everyone... I replaced my radiator because of a leak to the trans cooler lines. Radiator was busted. Was on highway yesterday ... Truck got to 65 mph and then dropped to 40mph. It did this intermittently driving home. So I pulled off highway and truck shut off at the red light. It started right back up then shut off down the road. Heard small whistling sound as well. Truck was fine before... Any ideas would be greatly appreciated

 

Whistling says vacuum leak to me - maybe you knocked a line loose in your repair? That could also account for the poor running.

 

Checked all hoses everything seems good. When idle purrs like a kitten. Could crankshaft position sensor be problem gonna change it out?