Reading out of "Product Enhancement for 2006 Model Year 2300 Combines". 2388 HP is up to 285 on the 8.3 l Tier three "Full Authority Fuel Control" (electronic control)engine. A 20hp boost, also a 20hp rise for a 325hp max. 2377 has 255hp with a 20hp boost and a 15hp rise for a 290hp max. Also a new heavy duty 3sp rotor gear case w_ helical cut gears for increased durability and strength, a new and stronger inverted spliceless rotor belt which is 1" shorter because of a repositioned rotor drive gear case. Every year it gets tweaked with small improvements, been doing this for 30 yrs, a big time advantage over the short time competitors.
