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Don't know about 904s (and very little about the later ones), but the trans designations say something about trans. 42RH decodes as 4 forward speeds, level 2 torque capacity, (something), hydromechanical actuacted. 46RH is 4 forward speeds, level 6 torque capacity. I'd go with the 46RH, if it becomes a choice of 42RH or 46RH.

As for the choice between 46RH and 904, I'd go 46RH as that gets you a tidier way of getting the overdrive.

Plus, though I may be out of left field here, some of the 42s have torque converter issues. My sister has a Jeep Grand Cherokee with the 42RE that will occasionally not stay in torque converter lockup driving on the highway (above 48 mph). I believe this is a known problem among dealers (yes, she had the TSB flash to the control unit). They refuse to look at the trans "because it hasn't thrown a code". (Whatever happened to good old-fashioned diagnosis?) My Durango had the same problem for a while (46RE trans) until I changed the fluid to Amsoil and put in a new filter. Problem solved in the Durango. Fluid and filter change in the GC helped a little, but didn't solve the problem. Maybe electrical, maybe the TC, maybe something weird about the Grand Cherokee version of the trans, I don't know.

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