1999 GMC Truck p0171/174 and small evap leak code

This truck belongs to a coworker, I spent about 30 minutes in the dark in the parking lot at work with my ELM327 Bluetooth scanner and the Torque app on my phone looking at it. I don’t have a whole lot of info but I’ll give you what I have.

History: 1999 GMC Sierra 258K w/ V6 (I think he said) of unknown size. Earlier this year he had about $1200 worth of work on it because it kept stalling. The guy that worked on it replaced the fuel pump for about $800 and I think did all the belts and a new intake manifold gasket. The truck was no longer randomly stalling on the road but still doesn’t run right and when cold if you push the gas the engine will stumble badly and sometimes stall. If you warm it up, it doesn’t stall but still stumbles a bit. It sounds like it has a miss at idle but no P030x codes were set. He said the guy that worked on it was never able to get the MIL to turn off but since it wasn’t stalling, he took it as is.

What I learned last night (all info from Torque application):
Drive status since DTC Clear showed all good except catalyst. (codes had not been cleared)
Short term fuel trim: I’m not sure how the sensors on the phone corresponded to real sensors but had 2 readings showing 80% trim and two readings showing 20% trim. So sounds like it’s dumping fuel.

I unplugged the MAF while it was running and it stumbled for a few seconds, then the idle raised to what sounded about 1200 to 1500 and sounded better. Doing that also set a pending MAF code.

I checked as many hoses as I could for cracks to smooshie-ness but all felt ok. (And I did tell him about spraying carb cleaner all around and listening for idle changes)

I was unable to locate the evap parts last night but since have read that they are near the tank with some parts visible from under the fender.

I didn’t spend as much time as I wanted monitoring O2 sensor data but Sensor 1×1 warmed up quickly and was bouncing above and below .5 with a wide range. 2×1 took a little longer but seemed to be working.
Sensor 1×2 and 2×2 were bouncing from 0 to about .35v. I didn’t check back after it had been running for a few minutes.

So are there any common items that seem to fail on this model (certain hoses that seem to crack more) or is it just hunt and spray? Also his PCV valve on the drivers side of the engine looked a but crusty but rattled when I shook it. I recommended he replace that because it’s cheap.

Regarding the small evap leak, how hard is it to get to the evap canister?

I don’t really know if he’s going to do anything I suggest he doesn’t seem like a DIY car person but I wanted to give him as much info as I could so he doesn’t dump another grand trying to figure this out. He does understand that the catalyst not ready will cause him to fail the emissions check for this year so he will need to get some of this fixed.