Is this buildup on the Oil cap and filler normal?

It's a start. Take it out longer on weekends and go somewhere. That motor needs to get hot for prolonged periods. You'll see the difference in the oil filler neck and cap once you start running it. What's indicative there... is also what's happening under your valve covers.

 

I would not lose sleep over it. My adult daughter had a hand-me-down ~2008[?] Grand Cherokee, Overland with a way overpowered, high mileage 5.7 HO v8. Anyway, she did lots of short trips, it had +250k miles and for the few years ~50k she had it and I took over mait. and repairs it had similar brownish residue that looked like baked oil. The oil filler spout and cap were longish like our V6 and I suspect some kind of off gassing and blow-by build up in that area. (FWIW: Original owner was very good on mait. but only used dino oil. The PVC system was a disgusting >50% clogged mess when we were fleshing up... No idea this is relatable; but maybe worth checking it out).

Anyway, that thing even though it was a MOPAR ran like a scolded dog for well over 300 miles with only the usual wear and tear parts.

My $0.02:
- Check PVC system
- use high quality (OEM) oil filters and full syn 0w-20
- periodic Italian tune-up's
- do a few short interval O&F changes
- Random engine flush ideas and process' are too high of a risk to do more harm than good; better off spending the time and money on OEM filters and top shelf oil
- Rust, an unfortunate accident or something stupid like a $3k ECM module will probably take the truck from you long before the engine calls it quits

 

Just an update: used the bore scope and everything internal is absolutely mint. No sludge buildup, only minor dark spots in the corners/crevices which honestly could have just been little oil puddles.

Super strange that the only piece affected was the oil filler and cap. I took those two off and cleaned them up. When i was cleaning away it REEKED of old slightly burnt oil so I’m thinking Hairless_Ape, Speedbird and one of the other guys are right and this may be a clogged up PCV, slightly low oil scenario combined with short trips. I’m just relieved the engine clean inside.

 

It’s just some corrosion from the prolonged sitting and not being driven.

 

Or the leftover residue from a bunch of short trips where the engine barely gets up to temp.