Problem seemed to start out of the blue, but I only drive the car on the weekends, and not every weekend.
I fire it up, idle for a min or 2, then off I go. For the first 10 mins or so, it runs great as it always has. After 10-15 mins of driving, anything above about 30% throttle will cause it to bogg/misfire badly. I can take the revs to redline at 1/4 throttle with no misfire, and idle is unaffected.
I was thinking that I may have a failing fuel pump (walbro 255) that is heating up and losing pressure, not able to sustain flow when I go heavy throttle. It's the only thing that comes to mind. What do you guys think?

 

It sounds like its time to run some tests. Check fuel pressure at +30 percent throttal.

 

measure your closed and WOT TPS voltage.

.45v closed
~4.6v open

make sure you map sensor is getting a 5v power. You should also check the voltage of the map sensor at idle.

 

how old is your o2 sensor ? I Had a similar problem and it turned out to be a bad o2.