I recently picked up Gangplank, and I'm loving him. I may even use him as my main over Warwick.

However, the builds I have been trying out revolve around stacking Crit and ArPen. While this build type works very well early game, mid to late game I fall off damage wise.

Any suggestions to build/rune setup that could possibly help?

Currently my build is Avarice Blade>Ionian Boots of Lucidity>Sheen>Zeal>Phage>Trinity Force>Cloak of Agility>IE>Finishing off with either an aatmas impaler or last whisper.

Rune setup is AD Marks, Armor Seals, MR/lvl glyphs and ArPen Quints

Hey mate. You can play him however you want, but a lot of people prefer to build him tankier than you have, that way you can stay in the battle much longer. That is what i do.

Items like frozen heart, frozen mallet, warmogs, Banshee's Veil etc.

If you want to build him crit, you have to go IE. Having 100% crits and 600+ damage Q's doesn't fall off, you don't need to go Trinity Force and Atmas.

But if you want to play him like other people suggest, most will say tanky DPS. Atmogs/Frozen Mallet, etc.

GP used to be kind of a 1 trick pony building lots of Crit and hoping for a big gunshot every 4 seconds or so.
After his rework he is much more suited to playing more conventially like a tanky DPS, which is good. Critplank literally just walks around, and every 4 sec he runs in, gets off 1 shot and runs back. Basically playing like a really bad AP carry with 1 spell and bad range.

I would recommend the Tanky DPS approach and check guides on Solomid on how to do so. I like Triforce for offense since it adds 160ish damage to every single gunshot you use reliably just from the proc. (plus the AD and crit boost). The slow proc is nice to have and triforce also adds the big movespeed, a bit of survival, mana, and AS for melee.

Besides triforce you will want tankiness for the rest of the build, including CDR for faster gunshots and more ULT availability.

I usually play jungle so it's AtkSpeed boots, wriggle's lantern (solid even on a non-jungle build), avarice blade, trinity force, and then from there it depends but IE or guardian angel are common picks for me.

here's all the types of plank you'll ever need to know

1. top plank, he sustains and builds like a bruiser

2.(not seen much) adc plank builds phantom I.E and goes man mode on you

3. support plank max's E and harasses bot lane

4. jungle plank viable jungler with a built in phage with grog soaked blade has potent ganks with his E speed buff and slow but mostly his high damage and ulti cutting off escape route

5.tank plank, sometimes bruiser plank goes top but they need more tank so gp goes frozen mallet war mog sunfire atmas for some dmg and that's all blokes.

p.s sense he scales so well in all aspects you can actually change him to tank adc or bruiser at any whim by mid game with just afew item changes
letting you effectivly addapt to your needs and situations for your team letting you counter

gp is a long time fave of mine riot tricked me into buying him with RP but he was so good i never regretted it haha

um i'd recommend doing atmogs and don't go for early trinity just buy the crit portion of ur builds first and getting the sheen. though that's assuming ur team doesn't need u to build tanky.

STOP BUILDING TRINITY FORCE total waste of space on all gangplanks if you have that kind of money 1 or 2 phantom dancers with ie and blood thirster and you will be 1 and 2 shotting people ALL game