At your idle rpm the transition from park or neutral into gear should be relatively soft, especially with that converter. Additionally unless you are on it, the gear change from first to second should also be soft. Sometimes if the converter clutches are dragging these events will take on an impressively harsh quality.
The converter lock up is tunable in the ECU strategy. It is possible the previous owner was fiddling around there and left it in a frisky condition. There are a number of aftermarket tuning products available for that engine trans combination. The one with the worst customer service is SCT. The HP-Tuners folks are much friendlier and easier to work with.
You might want to investigate aftermarket alternatives that have support for ECU controlled transmissions. One of the best featured and best priced is MegaSwuirt through
DIYAutoTune. They have a plug and play version for the SN95 cars that has all the TiVCT controls already in the software but not turned on. The ECU uses all Ford sensors or whatever you wish to use and could support your TiVCT system if you elect to keep it or it could ignore it if you chose to operate it that way.
The MS3Pro units that DIYAutoTune sells come with lifetime warranties, tuning software data logging software and cost the same (~$1K) as a tuning software only package from someone like HP-Tuners or SCT. You don't need the top of the line race unit you only need the #2 offering that comes in at ~$1K. If you want to use a Plug and Play model the price goes up to ~$1,350.
The big deal is you are in 100% control of the engine and trans tuning.
Ed