Most of the problems I've seen with trailer sway were the result of inadequate tongue weight. Have you eliminated that as a possible cause? I haven't heard of "push" as a trailer problem - what are you referring to?

On a completely OT subject, I dismantled a 200 SX and have a 2.0 engine sitting around that I need to get rid of. Would you be interested? (I also have a complete IRS set up for the car if you are interested, and you have the mounting points needed to make the conversion).