Without modification, the Canon EOS 550D (Rebel T2i) it is no suitable for infrared photography. Even with modifications, the sensor stack of some Canon cameras still seems to be insensitive to IR compared to other cameras. There is likely to be an element, in addition to the hot mirror, that blocks a significant amount of IR. According to a diagram in this mod guide you referenced, a possible culprit is the low-pass filter.
Even after modification, high quality IR filters are required.Any visible light reaching the sensor will confuse the camera, and the resulting images no they have bright foliage characteristic of IR photos. The following were taken with a 550D that had the hot mirror removed.