I like my mopar jake. I live right in the mountains so I am almost always driving on some sort of grade. I have tested it on a long 6% grade with a full load. You do still need the brakes but much much less. The jake is integrated via the powertrain computer. The trans will lock up the convertor automatically for braking. It then will unlock, downshift, relock, with the brake only coming off momentarily during the shift. You can then manually downshift to second with the brake still engaged and it will do the same dance as it does going from 4-3, all automitically. It is pretty slick.
This is my fourth third gen truck. I looked at some '01-'02s for ranch trucks and just don't think I can go back. The new ones are so much better to drive it is like night and day. If you stay stock or close to it the trans will last. my '03 dually is a work truck that tows heavy for a living. It has almost 100k on it and no trans problems, they are pretty durable. The steering and brakes are much better, the ride is better, the amenities are better, the list goes on. You can also get the old fuel economy if you stick to pre "600" trucks. both of my '03 HO's were/are in the low 20's empty.