Need help! New carb

[84step]

Hey guys could really use your help/advice on this one. Bare with me iam pretty new to this and this is my first carb swap. heres the deal, a friend of mine and myself replaced my old q-jet with a new Holley 670cfm street avenger. we got it on and somewhat tuned but what i have found is that if i have it i park the idle is fairly high i dont know the exact rpm because i dont have a tach but when it is either reverse or drive it goes down alot and the truck almost dies. It is driveable but when i stop it seems liek it dosent completley go out of gear and i have to hold the brake very hard or it will begin to roll, it also accelerated a little even when i do not have my foot on the gad pedal. Iam stumped so any help or advice would be much appreciated.