Garmin Split Times (as it appears on the watch)

It's a different measurement. The Garmin only shows increments of 5sec per km because that's probably about how precise it is. There's no point of it saying 4:03 km pace if the real value is 4:02.6 +/- 5sec. Might as well just say 4:05.

The other thing is just a difference of what's being displayed. Your current watch is displaying instantaneous pace (or averaged over the last X seconds), while your old watch showed your predicted average for this current km. Each has its advantages and disadvantages. I prefer the instantaneous pace because you can see immediately the effect of increasing your speed.

Just set it up to show lap pace vice pace and it will be just like your old setup.