That depends on a few things. The alternator is capable of putting out 130amps but it doesnt put it out unless you need it. So it will depend on what loads you have on the alternator.
If you draw more current than the isolator is rated at you will "blow" the diodes, if it is in fact diodes inside I do not really know but I think diodes are probably in them never cut one apart....yet
If your alternator is putting out 130 amps but the load is split between the two batteries charging circuits, say 65 amps each battery, then a 90 amp rated isolator would be fine.
As I said it all depends..... mainly on how the electrical circuits in your truck are split up. If possible run the high demand loads, like winches, lights, power seats, microwaves, hot tubs, etc
evenly split between the batteries.