The easy way is just to replace the complete truck, but after checking out the u25b truck design it was plain for me to see what was changed. Replace the Gear case/ with pins(9445011), 2-idlers(9445014) and drive gear(9445013. You also need to open the hole in the truck for the larger idler gears to clear. The Kato GP38 also used the same design and the gears were changed when the GP50 was released. Same can be done to the GP38 if one could find the parts.
Ah, that makes sense - thanks!
