What makes you think that your cramping has anything to do with electrolyte depletion? The cause of muscle cramping is pretty hard to pin point. It is unlikely that electrolyte depletion is causing your problems. Especially since you are supplementing. See article below:

Br J Sports Med. 2006 Mar;40(3):255-9. Links Sodium supplementation is not required to maintain serum sodium concentrations during an Ironman triathlon.

• Hew-Butler TD,
• Sharwood K,
• Collins M,
• Speedy D,
• Noakes T.

University of Cape Town, Newlands, Cape Town, South Africa. thew@sports.uct.ac.za
CONTEXT: Critical assessment of recommendations that athletes consume additional sodium during athletic events. OBJECTIVE: To evaluate if sodium supplementation is necessary to maintain serum sodium concentrations during prolonged endurance activity and prevent the development of hyponatraemia. DESIGN: Prospective randomised trial of athletes receiving sodium (620 mg table salt), placebo (596 mg starch), or no supplementation during a triathlon. The sodium and placebo tablets were taken ad libitum, with the suggested range of 1-4 per hour. SETTING: The 2001 Cape Town Ironman triathlon (3.8 km swim, 180 km cycle, 42.2 km run). SUBJECTS: A total of 413 triathletes completing the Ironman race. MAIN OUTCOME MEASURES: Sodium supplementation was not necessary to maintain serum sodium concentrations in athletes completing an Ironman triathlon nor required to prevent hyponatraemia from occurring in athletes who did not ingest supplemental sodium during the race. RESULTS: Subjects in the sodium supplementation group ingested an additional 3.6 (2.0) g (156 (88) mmol) sodium during the race (all values are mean (SD)). There were no significant differences between the sodium, placebo, and no supplementation groups with regard to age, finishing time, serum sodium concentration before and after the race, weight before the race, weight change during the race, and rectal temperature, systolic and diastolic blood pressure after the race. The sodium supplementation group consumed 14.7 (8.3) tablets, and the placebo group took 15.8 (10.1) tablets (p = 0.55; NS). CONCLUSIONS: Ad libitum sodium supplementation was not necessary to preserve serum sodium concentrations in athletes competing for about 12 hours in an Ironman triathlon. The Institute of Medicine's recommended daily adequate intake of sodium (1.5 g/65 mmol) seems sufficient for a healthy person without further need to supplement during athletic activity.

Huh. I guess the mass of information 'out there' that has tied electrolyte depletion and dehydration to cramping is what I've been going on. Are you of the opinion that there is no need for electrolyte supplementation?

I think he's saying your cramping is NOT tied to electrolyte levels.... but endurance.

I really doubt that is the root issue with my cramping. Yes, I do see that I am more likely to cramp later in a long session. But I have had a number of experiences in which I cramped up very early in a session. However, I've never really taken the cumulative fatigue of a hard week, etc. into account. That could possibly be a factor. All I know is that I've really got to figure this one out, because it is one of those things that can spell the end of a decent race very quickly.

somethign else to ask, are you cramping on the bike or run, and is this muscle (legs or something) or stomach?

on the bike i get leg cramps from pushing to hard of a gear, run i can get stomach ones from too much being in there from the bike or a meal. things to think about. and the harder i am going, the less i can have in there without stomach cramps.

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No stomach cramps to speak of. My cramping up is almost always in the pool and on the bike. Calves, hamstrings, and adductors, typically. And then I also get the foot cramp in the pool that seems to be very common with a lot of people.

Sounds like your muscles are too tight. See a massage therapist.

Foot cramps in the pool are usually related to calf tightness.

I am actually very flexible, which is why I started to look elsewhere for the root of the problem. I have excellent hamstring, quad, adductor, & back flexibility. My calves could be better, but I'm working on them.
One interesting thing to note, though, is that I've got a lot of trigger points in my muscles. I work on them almost daily and that really helps with regards to knee & hip issues I've had in the past. But I can't really say that working on them has helped the cramping issues.