1974 F100 starts to chug after 15 minutes driving although infrequently when driving at a slower pace. Would happen around the 70mph speed and stop chugs when slowed to 65mph.
Only have experienced this after it’s been warmed up, in the past 3 sessions of driving it will do this on freeway when driving 70mph, slow down to 65mph and no issue. Although, it seemed to have chugged once this morning when driving 45mph up a hill when during time engine was partially warm.
Any thoughts would be greatly appreciated