engine or transmission

I have a 72 ss chevelle and I just put a 496 in. I have 10lbs of vacuum at an idle. my problem is I can rev the car past 3000rpm in neutral but cannot go past it in drive. the stall speed is not engaging, but does go in reverse and first gear. I checked all the basics, it has fluids all the lines are hooked up and cables. I have a msd digial 6al system with a 6500 chip and msd distributor. the transmission worked fine before I did the swap and after the swap not so much..I have no idea what is causing the issue thanks for help..

Goose, first of all, welcome to the forum. Hope that you enjoy your time here, and that we can find an answer to your problem.

I'm not an expert by any means, but the thing that popped into my head as I read your post is the two detents of the torque converter to engage it fully - torque converter over the transmission main shaft, turn it as it slides back one "thump", then turn and push lightly for a second "thump" of the notch engaging. I expect that someone else will jump in here later in the day with more & better input.

1. Valve springs are toast.
2. Motor is not getting enough fuel to rev past 3000
3. Ignition problem.
4. Plugged exhaust system, particularly catalytic converter.

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Motor was just built, this problem started as soon as I put the brand new engine in...I can Rev past 3000 rpm in neutral and no catalytic converter