sweat testing

So I did some sweat testing a month or two ago.  First test was an hour long run in the morning which, at 75 degrees and 80% humidity, resulted in a 60 oz water loss (once I factored in what I consumed on the run).  This was somewhat alarming because of what I read the "averages" are (I'd seen 20-30oz/hour).  However, I guess this was not surprising because I've always known I was a sweater.  In fact, it could explain some of the issues I've had with past marathons because I was probably losing too much water weight by the end of the race and bonking badly because of it (my last finish was just under 5 hours, so I probably sweated more than I realized and didn't know what I was doing).

I'm now training for the Austin HIM which I would expect the weather to be at least a little bit nicer/cooler than what I'm used to training in (middle of summer in Dallas versus late October in Austin), but I'm also signed up for IMTX next May when the conditions could very well be what I've been accustomed to or worse.  Both are my first tries at the distances so I'm heading into unchartered waters for me.

I have gotten pretty used to consuming close to 60oz/hour at least at the beginning of my runs, but I'm sure I stop obsorbing the fluid at the rate that I need to in order to keep up and not lose more than 2-3% of my body weight over the course of a race.

I'm using IM Perform while training, water, salt tabs, and trying to consume 300-400calories/hour (which includes the IM perform) and so far have felt good (last weekend I did a 50 mile ride followed by an 8 mile run which I didn't have any trouble with)...the concern is what happens when I try to string everything together for the full distances...

Are there any other heavy sweaters out there that have ideas to overcome this?  Or at least some reassurance that consuming fluids at a high rate gradually will counteract this?