Having worked with off-road forest fire tankers in the past they are all tippy, as is every other 4 and 6 wheel drive fire service equipment. If you fight forest fires you need a machine that can run in the forest...off road. You ever see a fully loaded road tanker stuck off road? The mess after you drain them? Pulling a cat off the line to retrieve them? Not having that water? People can die from that. Not that you couldn't get a a 5 ton stuck, and it might take more than one cat if you do but it will still be a darn sight better. Ask any cement truck driver who has EVER been told "just back across the grass" about how fast and how bad road trucks can be out of their element. The truck will be a fine, no frills machine for you. In my opinion it will be no worse and better in some ways other built machines. I would say keep it on 1400's or smaller (I say smaller) for sure but beyond that parts are cheap and I hope it meets the requirements of your department for many years to come.
Sometimes I forget the way so many of you feel the need to pounce on people with questions like this. Someone asks if a 5 ton will work on his farm and you launch into these huge condescending lectures about how poor their choices are or (and these are my favorite) how everyone is going to die...somehow. Just tell the man yes, it will be slow, tippy and sucks to drive and leave it at that. For this guy, I buy a 5 ton, pull the bed and source a used tank. You could have a durable serviceable machine for $12,000 or less. 12 grand will not buy you its equivalent in a roadworthy machine. He needs to know real stuff. What is it like to change a tire in the field, what is likely to break, how often and how expensive. He needs to know that backing this thing loaded up a steep hill in low range will trash the transfer case. He need to know 5 ton specific stuff, not lectures on tanks. Yes other things could be better but they are not on the table, this is. He knows tanks, he works with tanks. He knows or he will learn. You guys know more about what it is like to live with these trucks, fix these trucks and drive them. Just tell them, don't withhold unless you feel the idea worthy. Tell them and let the choices be made by those that have to make and live with them.
I think the truck will work well. I can think of a few things that might help the project work depending on your application. Message me privately if you want.
Ken