GPS module good for timekeeping?

There is a data acquisition network of many units. Each unit is synchronized to the GPS. It turns out that the common OEM GPS modules have a nasty problem: the GPS time can suddenly jump by +/- 1 second once in a while. There is no indication if the time is stable or not. I tried several different brands and makes; all of them did that. The event looks random; I can't see any correlation with time or from unit to unit.

Can you suggest a GPS module with the good timekeeping properties?

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant