The first clutch is slipping.

1. Overhaul the clutch.
2. Refer to applicable Allison Transmission Service Manual.
3. Replace the piston seals.

Refer to applicable Allison Transmission Service Manual.

The piston seal rings are cut.

Replace the seal rings.

Refer to applicable Allison Transmission Service Manual.

The clutch-apply oil feed tube is loose or leaking.

Reset or replace the feed tube.

Refer to applicable Allison Transmission Service Manual.