Carlo,
If you need more than 1 fast input, then you need to go to a DL-06 as Eric suggested earlier.
If your looking for an output from the PLC within 3ms from the input, this may be an unrealistic expectation. However please review, and or test the immideate instructions (STRI, STRNI, OUTI) etc.. These instructions execute before the end of the CPU scan, and may assist in providing the required response time.
What is the purpose of your reading? are you counting cans, checking for out of round, speed indication?? Your answer to this question may help in figuring a workaround.
Mike