Sometimes if I am accelerating from 2nd to 3rd gear, mainly WOT, then happen to let off the gas then get on it again just as I change gears, my 350 seems to kind of hiccup or stumble until I once again let off the gas then get back on it. What things should I be looking for to diagnose this?

I had a problem similar to this in my 69 Charger where the accelerator pump was worn and not makinga good seal. Did you notice this after your car has been sitting for a long period of time? Mine was lucky enough to soften up a bit after I started using it more and more towards the spring/summer. If not, it might be time for a rebuild or it could be something as simple as dirt in the fuel filter shifting around and causing a partial blockage. Try the fuel filter first.