Sedan is a bit heavier...could play a role. They're all weak in the low-end...LS, GSR, ITR...b16's even more.

Likewise, there could be many other variables here...such as engine condition bwt. the LS and GSR's you've driven.

The b18b has a peak tq. at a lower rpm than the gsr and itr. That might be part of it as well.

Research it a bit...you'll see what we're talking about. If you're concerned, check the condition of your engine (compression test is a good way to start).