If the max weight is 6000lbs, Toyota should be offering you a 7000lbs forklift like Hyster and Nissan are. I hope you do not plan on lifting more than 2 feet off the ground with the Toyota. That is one reason why Toyota's initial cost is less.
Have the three dealers quote you on a PM service. That price should stay the same for every pm done. All PM's are oil, oil filter, air filter, grease, etc. At least you will know your fixed expense for service.
Take a look at customer support. Who do you feel will take care of you? Who have you used in the past? Are they in on this quote? If so, as long as they have been good to you, they should be first on your list.
For the amount of hours your running the equipment and with what you produce......my choice would be Nissan, Hyster, then Toyota.
All three make a durable truck and would work in your environment.
Keep in mind.......the Toyota comes equipped with SAS (anti roll over system) This SAS needs to be serviced every 6 weeks/250 hours. The pin on the swing lock cylinder needs to be serviced every 40 hours/replaced every 5 years. There are alot of sensors on the SAS system, such as mast height sensor, load weight sensor, tilt angle sensor, plus several actuators. This just means more money, more parts to replace, more downtime.
I don't mean to sound negative, I just want to inform you. I have been in this industry for about 15 years, to some I am considered a baby yet. I'm sure you will get more responses to this question you posted and they will bring up different issues than what I mentioned.
Good Luck!
Let me know what you decide.