I just purchased a 06 lbz with 18000 mi and looking at programmers and exhaust and was wondering which is better 4" or 5" from the turbo back? Also what are the pros and cons to either one? I am new to the diesel world and bought one due to having a 9000lb toyhauler to pull. Thanks for any input.

MBRP 5" turbo-back (down pipe widens from 4" to 5" and goes straight back)! Fits perfect, sounds great, looks great (see my garage).

As far as performance the 4 inch turbo back is the way to go, but if you want a good sound then the 5 inch is a good choice. The flow in a 4 inch doesn't slow down like it does in the 5, thus your engine gets rid of the exhaust gases quicker and helps with scavenging in the engine. This helps make a little more power and torque that you won't get with the 5. Thats my opinion.

4" is all you really need, but 5" does look and sound cool. It will not give you any extra performance over the 4" though. If you want a VERY aggressive sounding system, get 5". Otherwise, I suggest sticking with 4".

A 5" system will also change your powerband, moving it well above 2k rpm's whereas a 4" system will leave the powerband much closer to stock rpm's.