The same can be said for service personnel. Mechanics are as much an asset as your equipment. The difference is the mechanic's value increases when properly maintained. First, change the way you hire mechanics. In a tight job market, we tend to hire just to fill openings.
Little attention is paid to the potential a new employee has on generating income.
Remember your real income growth is not the equipment in your fleet. It is in keeping your equipment operational so it is productive. Next, make that 90-day probationary period count. Attend a 90-minute class each day that covers the basic knowledge needed to develop the required skills. These classes may last 30 days and then reduce to two 90 minute lessons per week.