problem starting 76 GMC

[screwballl]

ok this is a very unusual problem, it only seems to happen mostly when it is very high humidity or raining within 4 hours of needing to start it...
like this morning, it started fine but 2 blocks down the road it just died and wouldnt start back up... it seems somewhat at random but the moisture is the only thing i can think of...
what i've done:
replaced carb (needed done anyways Rochester was shot) has Edelbrock 600cfm elec choke remanu from Edelbrock themselves (9104??). This was done about 6 months ago.
replaced spark plugs, wires, distributor cap, rotor, HEI, module in dist within 3-4 months ago.

i can smell gas when i try to start it but its acting like its not getting spark. most everything spark related (that i am aware of) has been replaced. the only thing i can think of might be the vacuum advance or fuel pump? or maybe voltage regulator? i am not a mechanic so i can't diagnose these things but i can replace most anything on this truck.
I am not looking to spend $200 on a HEI or get $60 spark plugs. it is an old tired engine that still has miles left on it but i am not ready to put serious money into it (not liek i have a choice, the wife won't let me).
It is a stock 350, the VIN says this truck originally had a 6 in it but i am guessing someone put in this GM Goodwrench 350 sometime in the 80s or maybe very early 90s. When it runs, it runs excellent but this odd problem keeps happening at the worst of times like this morning on my way to work in the rain.