i don't much about this type of thing,but on a diesel i wouldn't run it above 4krpm's....the reson the lbz shows a longer rpm range is with the towhaul mode on it will hit 3800 to 4200rpm's at times,and if you noticed on the lly it has a dotted red line untill 5krpm's and when people would travel into the dotted red line it would freak them out so on the new ones gm removed the dotted red line but left the shift points the same,in the end that is the only difference that i know of...i have had mine to 4800rpm's but i would't suggest it,it will freak you out  hope this helps..you guys can correct me if i was wrong
__________________ James 
TyreBoyz Pulling Team
Pulling Truck called Late Nights
Puller/DD=04 LLY Reg Cab 2500HD,EFILive'd,Built Tranny and a fe fuel upgrades!
Business Truck
06 LBZ 2500 CC SB SRW,EFILive'd and a Built Tranny
DD/Beat Around
03 5.3L 1500 EC SB,Hypertech,Upgraded Tranny,Exhaust and CAI
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