Get a barrel kit if you don't already have one. With pump guns, you have to underbore, otherwise you'll have terrible consistency and that's if the balls don't just roll completely out of the barrel before firing. That's really the first and most important upgrade for any pump gun or Autococker.
Once you get a barrel kit and start underboring with decent quality paint, you'll probably get very good results over the chrono. Mine gets +/- 1fps over the chrono shooting Marbalizers through a .679 Freak insert -- I've never seen a reason to upgrade the valve, lol. But if you're not getting pretty good consistency a reg upgrade might be in order. However, I think the stock reg on that gun probably works just fine. But remember, the first thing that needs to happen is underboring
and even more importantly; good paint
. (you won't be shooting near as much.) A lot of people chase their tails when it comes to consistency, thinking they need a regulator upgrade/servicing when really their problem is bad paint and not underboring.
Other than that, what CrazyDriver84 said. You don't need a two-finger trigger on a pump gun, so a lot of times a slider frame just feels more comfortable/appropriate. I picked up a WGP slider frame for about $20 for mine, and I really like how it feels. That's not to say you can't use a 2-finger frame though. After that, go out and gog some fools!
*Also -- don't worry about taking flak for "upgrading a Trilogy." They are fine guns; and I challenge anyone to tell me otherwise after facing me on the field with mine.
And finally, pretty much any upgrade you put on it can later be transferred to a standard Autococker if you find one you like even better. (Except the pump kit itself; those are specific to the Trilogy.)