If you are sticking with the stock axles i would say 3" is a good lift. With that you can fit 31-33" tires. Any bigger and it might break the stock drivetrain. Also like someone said above, without going wider it will be a little more tippy the higher you go. On my 42 flatfender I estimate I have 1 foot of lift and 3/4 ton full width axles so it will be plenty stable offcamber and hold up to big tires. So to answer your question 3 inch is not too much but in your case i would say 3" is a good start.