I went with the SB dual disc on my 2002. I have a exhaust brake, so SB said to go with the DD. It can be a little grabby when backing as it does not like to slip very much. Normal shifting, no problem. May shift a little bit slower (NV5600) than stock, but I don't try to speed shift and usually double clutch. The DD weighs about 20 lbs more than the stock unit, so it doesn't want to lug down as low as before. Just have to keep RPM higher.

 

I replaced mine(nv5600) with the 1947-OKHD. Recommended by SB. I personally do not see the need for DD unless your planning to make alot of HP.
To be honest I only replaced mine because the Throw out bearing desinergrated, so I replaced everything. The factory clutch was still in great shape no heat marks or slipping (over 100,000 miles), and I have pulled alot of heavey loads. Just my .02

 

My stock clutch wasn't slipping on the pull, it was slipping on the downhill with the exhaust brake on. I could smell the clutch after descending an 8% grade for about 7 miles. My fifth wheel weighs about 12,000 lbs fully loaded. SB suggested the DD due to the exhaust brake.