On the chassis side of things, check out the specific unit, but I think the W series got a transmission brake added in 05, and a 6 speed transmission in 06. I also think Brazels might offer a retrofit option on the transmission brake for the earlier W series units. I think there were also some minor design improvements on the 8.1L Vortec engine that were introduced in 05.
2002 Safari Trek 2830 on P32 Chassis with 8.1L w/ 400 watts solar
2017 Jeep Cherokee Overland TOAD with Even Brake,
Demco Commander tow bar and Blue Ox base plate