1968 GMC 250 Inline 6 4.1L Chugging

[68gmcdude]

UPDATE..

I have done the following:

Replaced the fuel pump
Replaced the sock filter on the fuel sending unit
Replaced the fuel filter in the carb
Blew out fuel line from sending unit to fuel pump
Blew out fuel line from fuel pump to carb
Replaced rubber fuel line from sending unit steel line to fuel pump
Replaced vacuum line from distributor to carb
Replaced vacuum line from smog pump to carb
Confirmed vacuum advance canister is good
Confirmed vacuum advance arm is working
Checked vacuum at carb
Confirmed manual choke works properly
Confirmed points/dwell set properly
Confirmed timing
Confirmed RPMs
New exhaust (it was needed)

Going to have the carb checked again (was rebuilt last year). I don't know where to go from here...