1976 GMC C1500 She acts like a slug

i recently replaced the entire powertrain in my truck, to include axels so about the only thing left from 1976 is the body. 2 weeks ago upon completion of the re-instal i drove it around for about a week everything seemed to running out standing. i went out to start her the other morning the was no fuel in the filter>>> i cranked and cranked till she started with a little help from carb medic. i got the carb. set finally (i think) and i think i may have a vacuum issue. when i put it in gear and take off she's loud and thunderous... then she chokes like no tomorrow... any ideas??