Can it ever be normal to have trouble with speech/articulation after neck lift?

It is very early to tell whether your speech problems will be a long term issue, but in general, difficulty articulating words is not a typical problem after a face/neck lift. The local anesthetic should be worn off by now. There is certainly some swelling that could be causing this. The tightness in the tissues making certain sounds difficult to make could also be causing this, but the tissues will soften with time. Lastly, the facial nerves could be stretched or bruised causing a distortion in the facial muscles that help to produce sounds; however, if your mouth moves symmetrically, this is unlikely to be the issue. if you feel that this problem persists longer than a week, be sure to discuss this with your surgeon. this is an extremely unlikely 

Great question!   The difficulty in speech could be related to the repostioning of your tissues.  When the doctor tightened the neck that could account for some of the difficulty.  There could be local anesthesia as well but that usually wears off after 3 or 4 hours.  Rarely, one of the motor nerves could be weak after surgery.  These nerves help you purse your lips, smile etc.   If the nerves are working, then it is just post operative healing.  Hope that helps.