Is it the Torque Converter??

So, I got my 340 installed in my Barracuda a few weeks ago and have been running the motor in. I bought the engine built but don't know much about the specs other than I was told its 10.5:1 compression, mopar purple cam (no specs), forged pistons.
I added at 2000-2400 B&M converter not knowing much about the engine.

I'm wondering if the experts can tell me if the following symptoms are converter related:

• Drops about 300rpm from neutral to drive
• When I put it in drive you can really feel it with a firm clunk
• Just as I pull up to stop it feels like its still really straining forward and gives a little judder against the brakes

Going from a \6 to the 340 has been awesome, its like a totally different car. I'm not a track racer, just a cruiser (and stop light acceleration freak:lol:) but I'm wondering if a higher stall converter would make a difference to the above.

Any help greatly appreciated.