If you are going to do a lot of this, Segue has a SilkTest add-on called "Blue", or something like that. (Blue being IBM's nickname). Blue is fancy and allows you to assign tags to CICS screen fields. I also means you need to learn a new syntax.
I just needed to exercise a few legacy functions for integration testing, so I made a SilkTest interface for a 3270 emulator.
I tried using several different emulators, and I could not read the screen in any of them. I suspect that this is your problem too.
My workaround was to have SilkTest start the emulator and use the menus to log to terminal session to a file.
Whenever I wanted to "read the screen", I just read the last 25 lines that had been written to that file.
I have not done this is Silktest but I did do same in WinRunner and the add on they have that allows you to assign tags is worth its weight in gold - I would not want to set up teh tests without this type of add on
I have not failed. I've just found 10,000 ways that won't work" --Thomas Edison