Ford Repair: Engine rough and seems to be missing under 2000RPM., 2000 ford windstar, ford windstar

Question
2000 Ford Windstar 3.8l had blown head gasket. found head cracked.
Replaced complete gasket set and replaced bad head and had other head reworked at valve shop.
Before all this the vehicle was missing bad at all rpm's. Now it runs rough and seems to have a constant miss under 2000RPM. Feels and sounds like I am driving over rumble strips in the road. Just need some guidance what to check, have checked plugs wires and coils. Do NOT get any computer codes at all. Thanks.

Answer
You may have either of two problems going on or related.. the rumble strip feel is ohh so common, your feeling the torqu converter in thye transmission lcoking up. when this part gets worn you can feel the internal plates as the engauge. have your trani flushed by a reputable dealer or service station and have friction modifier added to the fluid. should eliminate this.