LS Swapped C10 Power Issues

[DannyBoy80]

Hey all,

Long-time forum member but been absent for quite some time - Just haven't had an applicable toy for several years. BUT, just picked up a new one that has been a dream for the past 11 years. Paid a pretty penny for it, as it's had a ton of high-quality work done to it and is unquestionably a show quality truck. However, I have some concerns about the power this thing is putting down... Here's the scoop on the powertrain.

-It's got a Gen IV LS iron block (assuming L96) with LS3 heads and a Texas Speed cam (specs unknown) along with a Delmo Speed "DELS Kit" that consists of a Holley 4150 4 bbl carb style mid-rise intake, Holley Fuel Rails, throttle body adapter (running a factory L96 truck TB I believe), etc. to make it look more old school, Speed Engineering exhaust manifolds, and a GM ECU with a MAP sensor (not MAF).
-Transmission is a 4L80E with Raybestos red clutch pack, and a 2,200 stall.
-Rear end is a QP Ford 9" with 3.70 gears

The previous owner that did all of the work (and provided boat loads of documentation for everything) also had a dyno sheet that showed it puts down 390 rwhp and 358 rwtq. However, even though it fires right up and runs quite well, the thing does not feel like it's making that kind of power... At least in the lower to mid RPM range.

When I go WOT from a standstill, it hardly spins the tires, and feels pretty sluggish until about 4,500 RPM, where it seems to wake up and pull pretty hard to 6,500 RPM. For example, just today, I used the Dakota Digital gauges 0-60 function to see what it would do, and I only managed a 6.3 second result. But, it went 60-90 in probably 3-3.5 seconds... Once it's in that upper RPM range, it doesn't feel bad.

Additionally, I've noticed, if I punch it while cruising at, say, 50mph, and kicks down into 2nd, it'll kinda "hang" at about 4,000 RPM for a good second+ before it continues climbing to redline...

Now, I do feel like the truck is running rather rich based on both the gas mileage (about 8-10mpg around town) and how strong the fuel smell is when it runs, and just from it sitting in the garage. It's potent!

So, I'm looking to the tenured LS swap folks for some advice/insights... Could what I'm experiencing be the result of running too rich? Could that cause my low-to-mid range power to suffer this much...? Are the conditions I'm describing indicative of this condition, or could it be something else?

I love this truck and am extremely excited about it but this situation has definitely put a bit of a damper on my excitement. Your feedback would be greatly, greatly appreciated!

Few pics of the truck attached. It's a beaut! Now I just need it to drive like it has an LS swap...