3.8l hesitation

i have a 1995 lincoln continental with a 3.8l engine. when driving down the highway at around 50 mph it starts bumping and jerking. also when accelerating from a dead stop to 50 it does it but not as bad, when i floor it it doesnt do it and it accelerates just fine... unplugged the maf and drove it still the same thing... hooked up a vaccum gauge to it and it's reading around 19"hg... changed the fuel filter, air filter, plugs wires cap and rotor, and also put some fuel system cleaner in the fuel tank... also sometimes has a rough idle, any ideas

it was a pin hole through the spark plug porcelain on the back left cylinder dont know if that is number 1 or 4, if anybody was wondering if i found out wat it was.