hot fix has broken all of these lol.
what is your build don?
It's not totally set in stone yet, but it depends on the battlegroup pick. Airborne is good but I'm starting to become a little more partial to the Armored battlegroup because US late game is mostly based around armor anyways. Making it so that your tanks are cheaper to build and cost less popcap ends up meaning that you can fortify and make caches easily in the late game, even with a large army of tanks. Plus assault engis repair quick, build bunkers quick, and can put down tank traps and barbed wire.
I play 4v4, btw, but my last game where I was fighting OST, my build was as follows:
Armored Battlegroup > Assault Engineers > Assault Engineers > MG > Sniper (I was fighting fallshirmspios this specific game) > Mechanized Support Center (I floated a little bit of manpower at this point and went for Mechanized Support Center, this is really touch and go, and if I had any inkling the enemy was going to get a light vehicle instead of simply spamming flak emplacements, I would have gotten a bazooka squad here. Your teammate will probably have to pick up your slack a little.) > M18 Halftrack > M3 75mm Gun Motor Carriage
After this point, the pressure is off you quite a bit, because the M18 and M3 halftrack work well as a team (their pathfinding is dogshit though). Hopefully you can get some good suppression and damage with your M18 and MG working together w/ sniper.
Get a good MG bunker + mortar bunker combo watching the VP if you can and then try to drive your tracks around the map helping your teammates if resistance is light on your side, the issue with this build is that it's very weak to being caught out of position so don't overextend. Plant mines like hell and build more units to counter what the enemy is doing as the situation unfolds.
Once you've got roughly 170 fuel or so, start building your T4. If your team has reasonable fuel control, you should have the sherman out around at the 12-14 minute mark. I'm not sure about the exact timing, but even if the enemy has skipped building lights, the sherman should come out around the same time as the 8 rads, wespes, stugs and wirbelwinds, and sherman can pretty handily beat all these except for the stug. If you keep your M3 halftrack alive, you should be able to keep the stug at bay.
The sherman can easily start bleeding guastatori blobs, and can do decent damage at range to panzergren blobs.
Play very conservatively with the sherman, though. The goal is to build another, and then upgrade with the 76mm gun. If you're able to keep those shermans alive, they can work wonders. You want to reach critical mass before you do any really ballsy dives. Without a flak 88, axis can't out-dps a wolfpack of 76mm shermans.
That's my opinion anyways. It's been working pretty well so far for me.