With all them hoses connected up to these darn things, be sure your all correctly plugged. Roy's idea sounds like a good start and it's cheaper then a mechanic. Install new plugs and check your mixture setup on them after a few runs. Could help with a lean or rich setup. The stock carbs are so cluttered up with smog BS, it's hard to tell what's what. 1st gear isn't much of a gear and depending on your driving habits, you may have to make changes around that issue. Every carb seems to act a little different in each truck, it may just be the characteristics of that wrecking yard carb. A good cleaning might help push through whatever the wrecking yard accumulated on it.