Pittsburgh PA to Raleigh-Durham NC.

Traveling from Pittsburgh PA to Raleigh-Durham NC. Is there anything that is a must try?

What is your intended route?

Yea a route would help us help you.
 
I would possibly guess I 76 to I 81 to I66 to US 15 south to Greensboro? 
 
If the Triangle Diner in Winchester were open yet I would recommend it on nostalgia alone but they are still doing restoration work. I hold out hope they will reopen this year.
 
If you do get anywhere near Richmond I recommend Hogshead Cafe , though get there early, lately there is a line to get in the (small ) place when it opens at 11:30, because it is just that good.
 
Also it is going to depend on what days you travel as some places are closed Sundays, Mondays, etc.

Assuming your trip will take you by/through WDC:
 
(Google away)
 

• Mario's Pizza House, Arlington, VA (subs, pizza squares; try BBQ topping) 
• Metro29 Diner, Arlington, VA (great fried shrimp; great breakfast, too)
• Hard Times Cafe, Arlington, VA; Alexandria, VA (chile & O.R.'s)
• Willard's BBQ, Chantilly, VA (many "styles" of BBQ, done well)
• The Quarterdeck, Arlington, VA (crabs 'n suds)
• Tune Inn, WDC (bar food & beer)
• Ben's Chili Bowl, WDC  (half-smokes w. chili; breakfast, too)
• Ray's The Steaks, Arlington, VA (steaks at reasonable prices)
• Ray's Hell Burger, Arlington, Va (burgers at high prices)
• Yorkshire Restaurant, Manassas Park, VA (Their "Top Hat" rocks; breakfast, too)
• The oldest still operating Five Guys, King and Beauregard, Alexandria, VA (if you've never yet been to a Five Guys)
• The Atlantis, Alexandria, VA (Greeks doing red-sauce Italian: the best!)
• Crisfield's, Silver Spring, MD (seafood)
• Peking Gourmet Inn, (Bailey's Crossroads area), Falls Church, VA 
• OMG:  forgot crabcakes:  G&M Seafood Restaurant, Linthicum, MD

BTW:  From my "list", Metro29 Diner, Tune Inn, and Ben's Chili Bowl have been featured on Cable "foodie" shows: Guy Fieri, Adam Richman, etc. 
 
And Ray's Hell Burger is President Obama's "go to" place when the Food-Cop-in-Chief is out of town.  He has also visited Five Guys and Ben's.
 
And speaking of Presidents, "H.W." and "W" were both loyal patrond of the Peking Gourmet Inn. 

79 down into WVA, then pick up rt 19 S. This takes you to 77 and you drive all the way to NC. Once in NC, take 74/rt52 to route 40E

when in doubt i always stop at an ihops

There is a BBQ on rt 15 a few miles south of the Pa line at the Emmitsburg exit, Old Frederick rd. and Rt.15. come on in and introduce yourself, I'd love to meet you!

 
When in the Durham area, go another 8 or 9 miles southwest to Chapel Hill.   In Chapel Hill, go to Sunrise Biscuit kitchen   Their chicken biscuits are, by far, the best we've ever had.   It closes at 2 or 2:30 pm.  No indoor seating.  it's drive through, or you can walk into the side door near the pick-up window, and order inside.  Take to your car and enjoy.   It's our top breakfast roadfood anywhere, and probably in top 5 or 10 of all roadoods, in our opinion.   
 
Mama Dips in downtown Chapel Hill has very good fried chicken. 
Roast Grill in Raleigh has very ood dogs / chili dogs.
The original location of Char Grill at 618 Hillsborough St in Raleigh has good burgers.
 
Make sure you root or the UNC Tarheels when in Chapel Hill.  ;) 
 
Glenn