Carburetor Woes

[1972K20]

I've got a 1970 C50 that had been sitting for about 10 years. Ive got the truck running, but it still has some problems. First of all, it won't run with choke completely open. It has to stay partially closed or it will quit running. It doesn't accelerate good and when pulling hills, it won't go over 15-20 mph. It starts and runs great, but it seems like the carb is stopped up.

Here's what I've done so far:
New fuel pump
New fuel filter (in-line, the filter at the carb was removed before I got it)
New fuel tank
New sending unit
Blew out the fuel lines with air
Fresh gas
Added Seafoam and sprayed carb cleaner in the carb
New air filter

Is the carb stopped up? What's the best way to clean it out?

Thanks!