If you're a fairly good Gears player, this Act won't give you any problems, solo or co-op (I did this particular Act solo). However, I think even the best of us had trouble with the lambent wretches; if they're not getting right up close to melee you they're exploding as soon as you shoot them and blowing you to pieces. You can find a legit way to beat them elsewhere online, but if you want the easy way out like I did then simply do the following:
Play through this section until you get to the room with the lambent wretches (there's carts all around the room). Then simply quit to the menu, continue your campaign on Casual difficulty and shotty your way through the wretches. As soon as you regroup with Cole and Baird, quit to the menu again and resume your campaign on Insane, job done. The rest of this section is fairly easy, and this is the only major problem of the whole Act.
If you're struggling with the Angry Titan chapter (the Corpser fight) then I can give a few tips. Speed is key here, immediately start shooting the body of the Corpser until it raises its legs, then shoot at the chin/face. It'll back off a bit, and again each time you do this. The wretches shouldn't start to appear until you get the Corpser onto the collapsible platform (you'll know when it's on there when you see a point-of-interest notification). You want to tread carefully here as the wretches can take you out in a flash, but luckily you've got more space to move around. I managed to finish off the Corpser without taking down a wretch; as soon as the point-of-interest pops up, shoot one of the destructible beams. Then immediately roadie run as far away in the opposite direction as possible (don't stop because those wretches are quick on their feet!) then quickly run straight back to the Corpser and shoot the other beam as soon as you're within range. I was getting attacked by the wretches as soon as I started shooting, but it takes a couple of hits to kill you.
Apart from that, just play through the Act as you would any other on Insane (slowly and carefully). Watch out for the two boomers at the end of the cart sequence (they're blessed with godlike accuracy on Insane difficulty), and take your time with the very end of the Act, the platform with the Theron guards on it. You're told to split up but you don't have to actually make a choice as to which way to go, so take the right path and stick with your team. Their torque bows are accurate as hell, and one shot is enough to blow you apart so be very careful. Your teammates actually do fairly well here (for once).
Shouldn't be too problematic, possibly the easiest Act to do on Insane.