Customer Request For A 5 Year Replacement Plan

Way too many variables not covered in your initial post like whether they are leased or owned, how long in the field, are they placed right (right sized for volume and speed requirements, are they centrally located or spread out over 5 states, etc. That being said, you are where you want to be. That is, you have a customer asking you to help them manage their fleet. A very conservative approach might be based on the fact that parts are only guaranteed available for 7 years past the last date the model was sold new. Keep in mind that good management isn't just when to replace but might also include moving equipment around to gain the maximum years of service.

The best 5 year plan would be to utlilize 60 month leases so that the equipment gets refreshed every 5 years.