First the #1 thing you want to do is either replace your purge canister or somehow drain it.
My friend's MR2 would not pass smog, and we worked and worked and worked at it, and finally found out that his purge canister was full of gas, maybe because he topped off his tank one too many times.
If there is gas in your canister, then it can easily be sucked into the engine and run it rich. When this rich mixture makes its way to your oxygen sensor, it will tell the ecu to lean out the mixture. But remember that the mixture is correct, but its just the added gas from the canister that is sending the wrong signal to the ecu.
If it is really rich then the ecu can very well pull plenty of fuel out and you would loose a lot of your power.
What happens if you keep your foot in it when it cuts out? If you keep the throttle WOT (wide open), then the manifold vacuum might be low enough as to not suck gas from the canister. Of course I recommend draining the fuel from there first, but you could try this to test the theory.