How steep is your hill? Are you not getting the elevation target because the trail doesn’t have much incline, or is the steepness restricting your pace and it just takes you that long to do 1k?
Depending on your fitness and training background you will likely get faster at the same HR as you progress through a plan. This could help solve your issue if the trail is sufficiently steep.
If you simply need a steeper trail, you may want to try indoors on a stair master to see how it goes. Only problem with a stair master is the elevation gain needs to be “adjusted” since the stair is falling away as you step up. Most on UA take the elevation gain and divide it in half. So for an hour you would want to see 2k of gain on the stairmill.