I have a 2001 silverado 5.3, I've had this truck for awhile but it's been sitting for 2-3 years besides a few times here and there when I've tried getting it running right in the past. I put it on the back burner cause I didn't need it but I wanna get it running now.

first I'll update you on the history
I blew the motor in it so we swapped the motor with another 5.3 with 150k on it, body has 250k. It ran decent but never thought it was perfect. Non the less I put about 40k miles on the new motor before parking it. The truck still runs and moves itself around the yard.

My issue with the truck is it starts up and runs like it did for the first 15 seconds even if I give it throttle, then it starts idling rough and and if you give it gas it wants to stall but fights through it with a lumpy acceleration. Once it gets to a higher rpm it'll hold it fine. It will stall occasionally when it drops back down to idle but most of the time will keep running. Now while trying to drive it it won't reach a high rpm and I can't get it above 40 mph. Currently I'm not getting any codes popping up but in the past I've had lean codes and misfire codes

Here's what I've done
New cats since I found one that collaped and clogged the exhaust on the driver side(currently has no muffler)
all new o2 sensors
new intake gaskets
new orings on the injectors
New plugs and wires
i remember replacing a few sensors in the past but can't remember everything that was done

 

Hello, MegaHurtsALot, Welcome to the Chevrolet Forum.

I would let the engine heat up, then try a compression test. Many times, on the older V8s, the valves seal beautifully,
while the engine is cold, but once they heat up, they warp, and create all kinds of hate and discontent. Also, check the air/fuel mixture.
This changes, as the engine heats up. Monitor your engine with a vacuum gauge, this could also be a vacuum leak issue.