340 problems

I put the 340 in the Dart last weekend and finally got a chance to run it last night and discovered some problems with it. I had expected high 12's and had planned on shifting at 6,300 or so. Instead I ran in the 15's and the car starts cutting out and popping at 5,000 rpm's. It is a slug under 2,000 and then wakes up until the cutting out at 5,000.

When you start the car up it want to idle around 2,000 until you put it into gear, then it goes down to about 800. You can blip the throttle and try anything you want but I couldn't get the idle down till I put it in gear. Weird huh?

It is a .40 340. Stock bottem end. Ported large valve J heads. MP purple shaft .484 lift. The following parts were robbed from the 360 when I pulled it. 750 Eddelbrock, weiand xcellerator intake, HV fuel pump, and MP distributor.

I am thinking Vacuum leak and was going to pull the intake today and reseal it. What do you think?