Darryll just as a guide, I ran 39:49 in September a week after doing 19:10 for the 5k.
If you can knock out a couple of 19 minute 5k's every week on a treadmill then you should have a sub 40 in you comfortably providing you pace yourself correctly.
If you start running 3:50/km for the first 3 or 4km as you have been doing, you are running 38:20 pace which is too quick.
When I did it I ran the first km in around 3:45 (adrenaline and the first km is always a bit quick!) and then settled into 3:57/km - 4:02/km all the way round.
Also, don't overdo it in the few days before the race.