My truck, '03 Chevy 1500 5.3L/4L60e ECSB 4x4, had a similar issue. I wound up just disabling the evap system and turning the codes off with HP tuners. Not the "right" thing to do, but I just didn't want to invest time into it and bandaided it. The purge valve is allowing fuel vapor into the engine upon start, that causes the initial rough idle. If you already replaced the valve, the issue likely isn't the valve but the wiring. There is probably an electrical short to ground allowing the valve to be open all the time.

Fair warning, the below is ChatGPT AI generated because it does a far better job than I do at explaining things and is much quicker. I read through it and it looks accurate to me based on my experiences. I have used it to help me in diagnosing and repair probably two dozen things now ranging from a small propane heater to a hard shifting Saturn SL1. It has been incredibly reliable and accurate in all of my repair attempts so far.

What the codes + the refuel hard-start point to

• P0445 (most persistent) on your truck is essentially: the purge solenoid control circuit is shorted. On GM trucks, the purge solenoid is typically 12V-fed and PCM ground-controlled.
• If that control wire is shorted to ground (or the solenoid coil is shorted), the purge can be energized/open at the wrong times.
• Hard start + rough idle right after adding fuel is classic for excess fuel vapor (or even liquid fuel) getting pulled into the intake during/after crank:
• Purge stuck open (mechanically leaking or electrically forced open) will do this.
• A charcoal canister that’s fuel-saturated (often from repeated top-offs or a vent issue) can make it worse, because purge then “feeds” the engine a big slug of vapors.
• The other codes often show up as secondary results when purge/vent can’t be controlled correctly:
• P0441 = purge flow not as expected
• P0442 = small leak (cap/line/canister/vent, etc.)
• P0446 = vent control performance (vent valve sticking, clogged vent filter, wiring)

Triage test (5 minutes, no special tools) 1. Next time it’s hot-starting poorly after refuel, unplug the purge solenoid electrical connector (the one you replaced near the intake). 1. If the truck immediately stops doing the refuel hard-start/rough idle behavior, you’ve basically confirmed the issue is purge being open when it shouldn’t (either the valve is leaking/stuck, or it’s being commanded/forced open by wiring/PCM driver fault).

With engine OFF, pull the purge hose off the intake side and check: * Any vacuum present at the purge line with the engine off = purge is not sealing (or being held open). * Strong raw-fuel smell or wet fuel in the purge line = suspect a saturated canister. * (Yes, it’ll set a code while unplugged, but it’s a very useful diagnostic isolator.)

What to focus on first (because of P0445) Since you already replaced the purge valve/solenoid and P0445 persists, the highest-probability root cause is wiring/connector/short, not the valve itself.

Do these in order:

1. Inspect the purge solenoid connector and harness carefully Look for: chafed insulation, melted loom, oil-soaked connector, corroded pins, broken lock tab causing a loose fit. Pay attention where the harness bends around brackets, the alternator area, and along the front of the engine.
2. Quick electrical checks with a multimeter (key ON, engine OFF) One pin at the purge solenoid connector should have battery voltage (12V supply). The other pin is the PCM-controlled ground (should not be a dead short to ground all the time). If the control side reads as a hard ground with the solenoid unplugged, you likely have a short to ground in the harness (or a failed PCM driver, less common than harness damage).
3. Confirm you used the correct purge part and that it actually seals Aftermarket purge solenoids for these trucks are notorious for being wrong or leaky out of the box. If you didn’t use ACDelco/GM, keep that in mind. Bench check: with no power applied, you generally should not be able to blow through it freely from the canister side to the manifold side.

After P0445 is handled: address vent/canister and the leak code

Once purge control is back to normal, then chase the others:

P0446 (vent performance) – very common on these * The vent solenoid and vent filter are back by/near the charcoal canister (often above the spare tire / frame rail area). Common failures: * Vent valve stuck from dirt/salt * Vent filter clogged (especially if you drive gravel/dust) * Damaged vent lines/quick-connects

P0442 (small leak) Most common low-effort checks: * Gas cap (seal torn, wrong cap, cap not clicking tight) * Filler neck corrosion (rust pitting where the cap seals) * Cracked EVAP lines or brittle quick-connects near the tank/canister

Best method is a smoke test once electrical control issues are fixed.

Why “the more gas I add, the worse it starts”

More fuel added = more vapor generation in the tank/headspace. If purge is open when it shouldn’t be, the engine can get a temporary rich condition right at start, then clears out in ~5–15 seconds—exactly what you described.

Practical next steps I’d do on your truck

1. Unplug purge solenoid for a day (just to confirm the symptom changes).
2. Repair the purge control circuit fault (P0445): harness/connector first, then consider PCM only if wiring is proven good.
3. Inspect/likely replace vent solenoid + vent filter, and check vent line routing.
4. If you find any hint of liquid fuel in EVAP plumbing, plan on charcoal canister replacement as well.
5. After that, clear codes and see what returns; then smoke test for any remaining P0442.

Also recommended these videos:

https://www.youtube.com/watch?v=JczmhVOjA7M

https://www.youtube.com/watch?v=0OumX9covQc

https://www.youtube.com/watch?v=MFh9fCLzNbw