I have full HK BiS, and as a 51 cab, I pulled 2282 single target dps last night on Garau. I was assigned to adds, but no small adds spawned...it was all big single ones in my corner. So realistically I would have been over 2.3k if I wasn't changing directions and hitting different targets.
If you're only getting 1.3k, you need to re-examine your macros and/or your build. Cab/Inq/Sent is the only build you should be dps'ing in as a Cab. Cabicar isn't dps, so make sure you're not running that God awful build when you're looking at dps numbers.