Carl's airplane's flatulence:

<My TSIO 550 with GAMI injectors, Slick Mags has backfired 4 times recently.>

A single cylinder misfire in a turbocharged engine will not produce a "significant" upset. Two things that I can think of will. One is preignition while the intake valve is open and the other is an intermittent short to ground of the P-lead. Both will produce a several revolution interruption of the combustion process followed by the normal operation you describe.

Check your ignition switch.
Check your plugs.
Check the distributor/points portions of your mags.

In that order.

Regards
Brent Regan

BTW, IMHO key ignition switches have no place in an airplane. They are expensive, heavy and fail with alarming regularity. They also provide NO security as they are trivial to hot wire. On a IV the door lock provides all the theft security you need. About 5 years ago my hanger was broken into and someone attempted to get my radios. A small paint chip, a slightly bent handle and lots of fingerprints were evidence of the crime but there was no other damage.

BR