I blew a head gasket in my 98 GT with 4.6 and replaced it with a 4.6 from a Mercury Grand Marquis same 4.6 but from a 95. It seems to run great and getting around 21 mpg but between 60-80 mph it has a miss to the engine. If I unhook the vac line to the EGR valve and plug the line, it runs great with no miss. The EGR valve is operating properly but I am still confused as to what might cause this issue. Is it possible that its not getting enough fuel with the EGR valve hooked up due to bad regulator or fuel pump?