Help! Intermittent loss of power

[79blazer]

Sorry this post will probably be long; I'm trying to be detailed about it. Background: About 3 weeks ago I rebuilt the carb in my ‘79 (added a second inline fuel filter too) and put in a new distributor and it ran great, gained 3 mpg even though the advance curve wasn't even perfect. I drive 1000 miles a week. I used to refill the tank when It got empty, 22 to 20 gallons each fill up. For the last tree weeks I filled up every day, until yesterday, when I let it run nearly empty. I tried to turn left onto a busy road and it surged, and almost died I eased off the petal it moved then hit the gas hard and it spun the tires. The gauge showed 1/8 tank which should be plenty, but I went directly to get gas and it topped off at 20 gallons. Gauge was right. Drove it, same problem. Pulled into a parking lot and it was running like it had a few bad plugs, lopsided idle but not skipping. Bought and replaced plugs with Ac Delco gapped to .045 and #3 was Heavily coated in oil and carbon. The rest were a happy sand color except 2 of them were a little more course and uneven color than the others. Had smooth idle and ran ok until 10 min later it went back into this “fit.” It surges:

75% throttle steady …… it will go-surge-go-surge-go-surge
pump the gas …….. it will go-surge-go-surge-go-surge
Pump the gas rapidly…….. it pretty much almost dies.
WOT……. it pretty much almost dies.
0% throttle, coasting……ok but has low vacuum
babying the throttle you will able to keep 30 mph
pull into a parking lot and it runs ok.

I disconnected and plugged the vacuum advance and turned the base advance forward some, (didn’t have a timing light in car) (the vacuum advance is way to high, have to keep the base advance real low to make up for that) WOT was good half the time and the rest of the throttle was not that good, and was inconsistent. I couldn’t find my screwdriver at the time so I couldn’t up the low idle speed at the moment (naturally because the total timing at idle was lower). Had no time to work on it when I got home. Slept.
Today it was ok and I restored the idle speed to 600 rpm and it was ok, then 2 or three hours later it suddenly did the same fit. Pulled over advance the base plenty and it still did it then it cleared up in 5 minutes and drove normal. Two hours later it threw another fit. Same exact symptoms. Then it was fine the last 2 miles to home. I was thinking fuel filter but I don’t think that would be intermittent. Any suggestions? Thanks