running rough after 20 min of driving HELP!

[cstm68]

my 68 with a 327 sat all winter long in the garage and was started about every 10 or so days, i tried to drive it last month and it would spit, sputter and die once i got about 100 yards. i replaced plugs, wires, fuel pump, fuel lines and filter, carb gaskets and vacuum lines. now it runs great for about 20 min then it seems to bog down and the idle gets cut in 1/2. now it is idling all over the board. what else could be wrong?

the carb is about 1 year old