400 and purple cam

Well there's your answer right there.
That 280 with a 3500, and 3.55s should be anything but tame.
However, by 3500 rpm,VP is nearly meaningless And so is Dcr. From 3500 on, the engine is just a big air pump.Even low-cylinder pressure is fast becoming a moot point. So if it seems lazy, try to find the choke point.
You may need to look at how the air is or isn't getting into the engine, and is or isn't getting out.You aren't still sucking hot underhood air are you?
But it may be that your engine is totally up to speed and yes, that you are just wanting more. This happens to me every summer as I acclimate to the power.
To help you figure it out, I suggest time trials. The fastest way to determine how much power your engine is putting out is to qtr-mile it and compare your trapspeed with known combos. And the trap speed varies quite a bit with the weight of the vehicle,and the power, but not much else.
Chrysler helped us in the 60s and 70s by compiling charts, that are still fairly accurate today. From those charts, we can get a pretty good idea of the power to weight ratios from the trapspeed. Not the ET so much,lol, cuz that is a very muddy pond.
And once you have determined your P/W is is a simple matter of back-calculating the power from the weight.
Just one example is this; at 400hp and 3600raceweight, you have a W/P of 3600/400=9.0, and the chart says this should trap at about 111 mph. If your car does not trap at 111, then either it does not weigh 3600 or it does not have 400hp; it's that simple. Of course there may be mitigating factors that can skew the numbers a tad,but by and large the charts work.
So once you know the engines true power level, and you think something is wrong, it's time to figure out where it's lacking. That may be a little harder to do, and may cost a lotta money to rectify.
But just throwing a cam in it, IMO is not the best idea.Especially with an unknown compression ratio.

Also keep in mind that a streeter is a completely different set-up than a race-car. Many, many sacrifices have to be made to get a nice streeter. Or perhaps I should say that a racecar must be a much more focused combo, and that the streetcar has a much broader operating environment. The 292 puts your streeter into the realm of racecar, in that the TC and gears have toi follow it, and the engines best operating range becomes very focused and somewhat narrow. Now the 3500TC is the first concession to that, as will be the 3.91s that you already have. And the very high operating rpm requires engine oiling mods to survive. If you just slap the 292 in there and start drivinig it into the deep 6s, the rodbearings won't put up with that for very long. Just a couple of seconds of detonation and you get to start all over.
But the 292/3.91/3500 combo is now limited to cruising at about 55mph, so it's become a city car, and a weekend warrior cuz the price of gas will really put a damper on the DD aspect. So there's nothing wrong with that except you got all this money tied up in a project that sits mostly in the carport all the time.
So just to remind you, there's more ways to get power out of an engine than just to throw more cam at it.
One of the problems I found with the 292 was that, to get the best out of it, the engine had to be really revved. Like the power didn't start until about 5000 and didn't really end, even at 7000 it was still pulling. Well this window from 5000 to 7000 with 3.55s occurs at 44 to 62 in first gear, and from 74 to 104 in second (automatics). So ok, it pulls really hard here, really hard. But really it has become a one-gear streeter, at WOT. Where you actually drive it is mostly not at 5000 to 7000. Mostly it will be doing say 20 to 40 mph, maybe occasionally 50. So really wouldn't you want the power to be there? I know I did and ditched the 292 almost as fast as I could.
To get the power from 20 to 40 is a real eye-opener. You might want to sit down.
With 3.55s , 30mph is about 3400 in first gear. Trying to get power out of a 360 at 3400 is a real chore, but the window from 20 to 40 is from 2200 to 4400. So this is where your 3500TC totally makes sense. But your 292 is way out in left field, as is the 280/484. No if the 3.55s stay then you want a cam to put the power where you need it,namely 3800.
But let's say you give a rat's behind about hiway cruising or economy. So work it out with the 3.91s. Now, the window from 20 to 40 is from 2500 to 5000 in first gear. So you want the power to be at about 35mph or 4400. Ok the 280 cam is out! Again.
So lets back up the bus, and just start with the 280 cam and see what gears we do need to work with it. Ok let's say the 280 is peaking at 5400 in your X-headed monster. This will take about 4.56s!in the window. Lets do the math. With 4.56s;20mph =2900, and 40 is 5800, BadaBing! Now with your 3500 TC, you may get away with 4.30s, which will at least get you 50mph revved out at the top of first.
My 292 combo an 4-speed liked 4.30s to 4.88s
But here's the rub;
If you get tirespin then all this means chit. If your tires spin from 20 to 40, it almost don't matter how much power your 360 puts out, it won't ET well in that zone,so you might as well put it back to stock,lol, cuz the difference in ET from 20 to 40 is just a couple of blinks of an eye, allbeit accompanied with all kinds of smoke and noise.
Yeah so there's my 2 cents.
Except to get a timeslip; which will spit out your W/P and tell the tale.