Running rough at low rpm

OK, So Temps started rising from 70's to above 100 here in Phoenix recently. My usually smooth running ride idles fine, but started stumbling at low rpms and lower gears with no load on the motor, upshifting and putting more load on the engine and freeway speeds it disappears. around 1500 rpms more or less.

Keep in Mind I'm running just an HEI and MC2150 Carb.

So I go through the usual checks
Timing, good 8*
Vacuum at dist good, advance working good.
No other vacuum lines left except heater door, broken at firewall, capped.
No apparent vacuum loss at carb mounts, spacer, etc.
Idle mixture screws, richened a little, helped a bit

Next on the menu check plugs, pulled 3 then quit since they obviously need replaced, Pic attached,Replaced 6 mos. ago. I would say they are ash fouled, but somebody Please chime in your opinion and cause / remedy. I did run a couple cans of Seafoam through the fuel tank over the last few tanks

Also i bought the "turbo titanium" on the advice of my friendly auto parts counterman, Then promptly read some folks prefer the plain basic types.