That may be the case, but I have swapped the transmitter and receiver on my Granite for the FS GT5 that I use on my TRX-4 and Slash 4x4, and the lag is still there. I have also run my Slash 4x4 on the SLT3 with no lag, so even if the transmitter makes a difference, there isn't a big difference...
It's something with the ESC. I have the same problem with my Granite BLX V3 even after turning the punch all the way up, the lag is still there (a little less, but still very noticeable). Unless you change the ESC, I don't think the lag will go away.