The name of the improvement project in Chicago is the CREATE program, not Chicago Gateway. I see that Amtrak has used the Chicago Gateway phrase, but that is not an official project name. There is the Indiana Gateway project which consists of 8 separate additional crossovers and 2nd/3rd track segments that will reduce congestion for the Michigan trains and the Capitol Limited & Lake Shore Limited, but that is in Indiana, not the Windy City.
As for CREATE projects that have helped on-time performance, the highest profile one would be the Englewood Flyover which seperated a rail-rail crossing and has removed a significant delay point for the Michigan, CL, LSL trains. There was another project installing signal upgrades that I recall was completed a year or two back that helped the Cardinal on it's route in and out of Chicago. Likely some of the other completed CREATE projects have reduced delays and fixed chokepoints for Amtrak, but how much they have helped has not been broken out as far as I know.
The big CREATE projects that would help Amtrak reliability and reduce trip times are the 75th Corridor Improvement Project and the Grand Crossing, but both of those projects are effectively stalled waiting on funding.
