Here's the good news. You're playing Orks and basically they haven't changed. Keep with the last version of your list and give them a go.

I still want to expand the list to 4000 points though so not sure what to add in to make it more competitive.

Will give a few 3000 point games a go and see what the list feels like...

Kris

My tip on what to try and get hold of would be flakkwagons and several of them. Their AA is not great but if you spread them out throughout your army, then at least some will hit eventually. The ones FW sell are quite nice.

I'm a big fan of the stompas in general and the supastompa mob in particular. Get those.

Fightabommaz are great, and greater in bigger formations. I've never tried the 9 FB formation but I'd suggest you try and get a few more. I you take the list to 4000pts, then I'd suggest two formations, perhaps 2 x 4 or 6+3, or at least increase your current formation above 3.

Other than that try and find some suitable battlewagon minis or perhaps try and converte some. Here's how I did mine. I like to play with a mechanized mob, the mobility is nice.
Lastly grotz. I always add a few boyz + free grots to my boyz mobs. Grotz are great.

Cheers