Truck feeling really heavy

[Low84]

Whats up guys. I took my truck out for a spin today (hadn't moved it in MONTHS so it had a little bit of old gas in it). I put some 87 octane gas and went to try it out. It is feeling really heavy at the lower rpm's/off idle, its not responding how it should to throttle. Uptop it feels strong and fine, but down low its almost like its going at its own pace.

I'm thinking the carb (stock quadrajet) tuning may be a little off Does anyone have a link that teaches one how to tinker with the air/fuel mixture? Or could it have bee the old gas (Its gas is around 4 months old) but it was a quarter of a qarter tank of gas left in it. Anybody else have any suggestions as to what might be causing this.

Here is a vid, I got flowmasters and you can hear the engine not really reving up quick. At the begenning I didn't really lay into the gas, but I was still on it pretty good, around 1/2 throttle maybe more. But the engine is climbing up really slow. It got to me and I floored it right before the hill, felt stronger there. But still the low end is horrible, it wasn't like this before