Well, obviously, I feel pretty strongly about SB's products. And it's a free country, so no one can tell what to do... ... . in saying that, the 1st gen clutches are 13", and they tend to hold better than the stock 2nd gens with the 5 speeds. Valair makes a decent product, I think, but I think there are better out there. And the power limitations on the 1st gens help the clutches survive a little longer.
Honestly, I don't think 1,000 hours is very long for a clutch to last. I haul heavy, too, and on my '93 and '97, I don't know what kind of mileage they get unloaded, as I've never run a complete tank of fuel through them without a trailer or load of some kind, if that gives you an idea. I've got well over 1,000, probably close to 1500 hours on my '97, with a ConOFE South bend, and I haven't had any problems with it. I had well over three times that on my '97 prior to putting the power mods and new engine and 6 spd, and that was a factory clutch, which I had slipped a time or two, so I backed the fuel plate down so I didn't have to pull it out. I believe I had 189k on that assembly, and only pulled it due to a minor oil leak on the rear main, and a fried NV4500.
The original clutch just came out of my '93 when I did my NV4500 swap a few months ago, and not because it was bad, but I planned on some mods, and didn't want to do it again. That clutch has spent most of it's life in 2nd and 3rd gear, so hours are wayyyyy up, probably well over 5-6,000, most in 4 wheel drive pulling a 16' half-top cattle trailer in deep sand with a horse or two in it. And taking off in sand is no fun. It magnifies a loads torque on the clutch and strains just about everything. Add 3:54 gears on top of that..... I believe those are SAKS clutches... . I'll check here in a bit, it's still sitting in my shop. I indexed it before pulling it apart, and bolted it back together for storage, so if I find a "project" truck I might have some parts... ... anyway. My first Cummins, my '89 D350 CC, ran 585k on the original clutch. I'd guess that at close to 15,000 hours, but power mods were only done by Cummins when I had to put a pump on it after the first 450k.....
Just some first hand experience. I'd look around for what's available for the 1st gens, and if you only got 1,000 hours out of the Valair, I don't think that's very good service, but then, I don't know how you drive, either.