I'll confirm what Banshee said earlier: it's a timing problem, or rather a lack of timing advance.
Your engine gives all the signs of being in good shape. Steady vacuum readings mean no burnt or bent valves, 450 rpm in drive with no missing says the same. If you want to make sure, get a leakdown test done.
One thing to check that Quenton mentioned is the timing chain. Easy way is to remove the distributor cap and watch the rotor as you manually turn the crank back and forth. How much you can turn the crank without turning the rotor tells you how worn the timing chain is. If you have the timing mark on the harmonic balancer at TDC, you can read the number of degrees of slop you have. You'll be able to feel when the chain tightens in either direction as you turn the crank. At 72,000 miles if it hasn't been replaced yet, it will be loose. Change it to a timing set that has multiple keyways in the crank gear and set it at 4 degrees advanced, as Quenton also stated.
Next, do as Banshee has stated several times, get your distributor sorted out properly. The fact that your engine pulls fine once the rpm is up says that your mechanical advance curve is slow, meaning that you're not giving the engine the advance it wants soon enough. If you have a tach and an adjustable timing light, you have a distributor machine. And it always takes several tries to get the curve right, whether in the car or on a proper distributor machine. Try the combo that Banshee suggested.
If you don't feel that you want to recurve your distributor, get someone to put the distributor on their machine and tell you what you have now, and get them to recurve it to the specs that Banshee gave, all in around 2500 rpm. Get them to set your vacuum advance to start at 6" and end at about 12" vacuum. Have them set the end clearance in the distributor at .010" to .015".
This next bit is for the guys that do their own recurving. I do the recurving at our shop, and I have yet to put a kit into a distributor and have it produce a decent curve without having to reprofile the cam (center piece) by grinding. I have a template that I grind every one of these to before installing it in the distributor. This gives me a smooth, linear curve, instead of one that goes in steps. The other modification that I do is to weld the slots that the upper piece moves in, to limit the total amount of advance to about 22-24 degrees. This is so you can run about 12 degrees initial timing and end up with about 36 degrees total timing once the curve is all in. I weld the "slow" end of the slots so that the springs have some preload on them. Makes the springs a bit easier to select and the curve more tunable. Yes, the weights seem to stop the curve without the welding but at high rpm the timing starts moving again.
The torque converter in your Dodge is draining back into the tranny, and the pump needs a bit of time to refill it after starting before it will work correctly. If the torque converter on your 'Bird isn't working right, it won't be "converting" or multiplying the torque from the engine, and will act as a fluid coupling only. Could be but I don't think so. Take care of the timing chain and the distributor first.