Suggestion get a 5 year full maintenance agreement proposal from each company you are considering. Use 1500 hours per year usage (unless you know how many hours per year your trucks actually run) for a single 8 hour shift. Let the lift truck folks survey your operation to determine if is "normal & clean" and no unusual floor conditions (cracks, long ramps, etc) or operations like "pushing or shoving things. Ask what the overtime rate is cost per hour, how often overtime hours are determine (monthly, quarterly, annual or at the end of a contract? Also ask how & when the hour meter is activated (at key on, via engine oil pressure, operator in the seat, etc). Oil pressure activated is fair for both parties.
Ask what is not included (like seats, tires, lights, abuse etc).
Inquire as to what happens if "suddenly the economy jumps start" you need to go to a two or three shift operation.
Ask how often they will give you a performance report/audit (actual against agreement) on how you are doing against the contract - every 90 days is not too much to ask for..
Add any other bits you wish.
This should give you an idea what the cost of ownership may be