Bad gas, carb float or ?

[don t. - 72gmc]

1970 GMC Sierra, 2500, 396/400/402 cid, th400 w/factory air that needs a recharge.

About 18 mths ago, filled tank and added Seafoam a bit strong for winter storage.
Ma got sick, and for all intents truck did not run in 2012. It never left the barn.
Month ago I got er running.
2 weeks ago, rebuilt q-jet carb.
1 week ago I fixed gas leaks
This past Sunday morning she was running good.
Sunday afternoon wife and I wanted Ice Cream. Climbed in and she ran like ship from the moment she fired. No choke, pump pedal to get on road, would die almost immediately. Would restart, the same way, w/o a problem.
Just 10 minutes ago she again runs good, albeit a bit sluggish, after a 5 mile trip. Never got that far Sunday afternoon.

I've got 1/2 a tank of this Oct 2011 gas and Seafoam.
If it is bad gas, what is the easiest way to drain?

Maybe the float is getting hung up? I know it was seated correctly before I buttoned it up.

Kinda confused with the good truck/bad truck.

Thanks...don t. ....