C2500
The computer tuner guys I think will have you covered.
However lets look at the basics first.

You are not getting what you expected to.
First lets check the timing
Are you running pump gas or REC90 race gas
On modern pump gas up to 10% ethanol you can set your total advance to 38 manually by bringing the motor up to 3000 rpm for 30 seconds and then set timing to 38 degrees. Then disconnect the timing bypass under the dash and check timing at idle should be about 10-16 degrees. On race gas the same, on REC90 set it down to 35 and 10.
Then check your vacuum on a 383 even with a medium cam the vacuum should be greater than 26 inch HG.
If lower increase fuel pressure bit and check again you want to get the highest vacuum you can obtain at idle.
Now if you put a vacuum pump on the EGR valve and pump it up the idle should get funky and vacuum go down release the vacuum pump and it should recover.
If not then yank the EGR and replace, on the 2500 you need the EGR to protect your top ring lands.

If the old motor was puking oil your cat and even the resonator can be clogged if the same pull the O2 sensor and put a adapter in with a 0-10psi gauge with a long hose take the truck out run it normal and look at the pressure gauge it should not exceed 2 psi if so replace exhaust before you ruin your new motor.

Another issue that a lot of truck owners have is the lame fuel pump on the trucks since the stick motors were only 200 HP the bean counters put the cheap fuel pump in 36 dollars at GM dealers.
I changed mine out to an AC Delco EP376 and set the fuel pressure at 18PSI.
Now the truck is crisp and pulls all of its 200 HP working ;-)
Before complete failure mine had no symptoms and the previous owner did not notice.
When I changed mine the fuel pressure was below 1 psi I measured on a digital gauge so swap out the pump.

Once all good then look into the tune.

I have played with the 7.4L 2inch TBI unit no good for less than 400 CI it tends to dribble instead of squirt at idle and low rpm and you get a bad BOG even if you raise the enrich table all the way. The bigger TBI was designed for the BBC not the SBC and kind of sucks on a small block.
The stock TBI unit with all of the Mods is good for 670CFM the 383 naturally aspirated is good for 450HP under 6000rpm.
With 6lbs of boost easy 600hp.

To get the 450HP hour available the intake and fuel system has to support 9.16Gallons of Gasohol per hour at 14.2:1 and 130 gallons of air per hour In and out.
Full rich 110 Gallons per hour full lean 156.6 Gallons per hour.
You need 55.62 PPH of gasohol to make 450HP.
The stock injectors new flow 55PPH.
Lots of guys are putting the 7.4L injectors (92PPH) in and trying to get an acceptable idle they dribble at low pulse width and actually are limited to about 5300 RPM until full open.
They are quite a bit slower reacting and the minimum injector off time is relatively longer so poor economy slower throttle response.

It reminds me of when the dominator carbs came out and a bunch of guys upgraded their 650 double pumpers on stock SBC to 1000 cfm Dominators because more was better. I actually got a couple of those pink slip titles back in the day.

Remember Nascar makes 900 to 1100 HP on 104 octane pump gasoline from a mandated 348 cubic inches through a 13/16 throttle restrictor plate.