440-6 Challenger temp thermostat

My 70 Challenger 440-6 has a 180 degree thermostat in it now
I have serge at cruising speed when it warms-up after 15-20 minutes
Should I try a different temp stat, or look for a electrical problem ?

"sounds" like your experiencing a lean surge, what size jets and power valve are you running? have you ever set the outboard carbs fuel/air idle mixture screws? as well as the center carbs idle/air mixture screws?....and where's your timing at, initial and full?