Engine missfire?

[Spencer hastings]

misfire? Guys have run into a small issue got my tanny rebuilt out back in New cam valves and lifters first test drive I got this like sneeze type lose of power . Almost like I hit a brick for a half of a secound happened a few times looked under hood realized that the vacume line too carb wasn't re attached after turning. Took it about 30 miles out never happened again then comming home it happened seems at about 1200 rpm if I ezz into the throttle it will be like boom no power no acselirater like I hit a brick wall but only last a secound. Happened twice comming home. I do have a manifold leak I have to fix but don't think that's it any one elts curiouse to weigh in I originally thought maby a vacume leak but not sure any more on happens sometimes . New plugs wires and coil pack too I attached a link below on the carb I have in it thanks

1985 gmc c2500 350 v8 with holly carb
700r4 transmission
https://www.summitracing.com/parts/QFT-BR-67270/reviews

 

[Spencer hastings]

You guys just as stumped as me?