Truck Repair: 79 Chevy P/U, vacuum leaks, minor overhaul

Question
The truck has a 250 with three on the tree.
Bought it new in Nov. '78.  Carburater has been rebuilt twice.  The second time was unnecessary because the problem was the automatice choke.
In '94 did a minor overhaul.  Since that time the milage has been terrible and only drive the truck on the weekends.  Use to get 17-19 mpg.  The carb is a two barrel Rochchester.
Would it be beneficial to rebuild carb?  Does only driving on the weekend cause the low mileage?  Is there some other carb that could replace the Rochchester?  with an adapter?

Answer
Hello Rick,
I am sure different carbs can be made to fit, but if you got 17 to 19 before with that carb, then you should be able to do it again.
Timing and vacuum leaks is where I would concentrate.
Advance the timing till it clatters a tiny bit when accelerating up a hill, then back it off a tiny bit.
You say a minor overhaul, and since then....
Would that have been a valve job? Did you replace the cam, and could you possibly have gotten it one tooth off?
The weekend driving wouldn't cause the problem.
Make sure the EGR valve is closing completely.
Van