Now when my 78 Stepside was falling on its face, I was tired of messing around with the old Quadrajet. So I bought a brand new Holley Truck Avenger (670 CFM). Supposed to be bolt on and go more or less, so I bolted it on and went-but not very well. It idles way too fast and is adjusted all the way down. Also, my top speed has gone down from over 80 to about 60-65 where it starts acting like it's starving out. Since I had to use a adapter plate, I'm thinking vacuum leak. I would like to take it back apart and use some sealant, but someone told me not to use silicone. What should I use? I would like to think that it is not the carb, could a leak cause all this? Could it be in the intake?