Yah, if you want tough AI, try TMO. But be wary, they are nasty.
In a bit of a bad mood with the game myself, atm. But that's more from my own mistakes than anything else. But still, be careful with TMO. Escorts are much more tenacious than in stock. Especially in late war.
I'm probably doing something wrong, but late war I can't get anywhere near convoys or task forces unless there's a heavy storm. One reason I kind of prefer early war play.