Could be both. Do a
complete tune-up, including good to excellent quality plugs, cap, rotor, wires, & coil. Don't skimp on the wires or plugs, get the best.
If you're still having problems, don't get frustrated! Instead, be sure the carburetor (I'm assuming either a Holley 1946 or Carter YF[A]) is getting gas by replacing the fuel filter. Replace the air, breather, and PCV filters, also, as this will help idle an unbelieveable amount sometimes. The idle screw could need adjusting, but if you don't have experience with carburetor tuning, DON'T mess with it.
Another problem I've had with those carbs (Holleys) is the hot idle compensator valve. Have it checked, too, if you have one.
The choke could be sticking shut. Take a bottle of good carb & choke cleaner and give it a good shot to get the gookies off. Misadjustment of it could also be a problem.
The transmission could just be taking a crap on you. You didn't specify what kind you have, so I can't suggest anything right now.
As for timing, check with a timing light and adjust accordingly. 14 degrees BTDC is good for a little more "get up and go".
Good luck!!!
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Capri306
1979 Merc Capri
3.3L (5.0L coming soon!) --- C4 --- 2.73
"...burn your face upon the chrome!!!" -- Metallica's "Fuel"