New Holland T8010 Manual page 1557

Transmission regulated pressure accumulator is discharged
Cause:
The transmission controller monitors the regulated system pressure. If the pressure drops below normal range
during shifts, this fault code will be recorded.
Possible failure modes:
1. Transmission regulated pressure accumulator is discharged (most likely).
2. Extensive internal clutch leaks (Rare case).
Solution:
The transmission regulated pressure accumulator plays a big role in Powershift.
If the shift quality for all shifts is noticeably deteriorated, it is a good indication that the transmission regulated
pressure accumulator is discharged.
If the accumulator is fully charged but the fault code still appears, there may be extensive internal clutch leaks.
Section 55 - Electrical System, Controller - Chapter 4
FAULT CODE TRANS 78
55-4-30