Sorry to bring this up again but,

I had time last night to check the tranny mounts and they all seem fine. Basically the tranny will jump into gear P-D, P-R, or D-R. It gives a violent clunk but thats it. It shouldn't be jumping into gear and I'm concerned that it'll get worse.

While driving, it only shifts hard once its warmed up, when it's cold it shifts gears smoothly. It doesn't slip or hesitate, just shifts hard.

I was on quite a few jeep forums for those who have the 42RE and some say it's the speed sensor - but this doesn't explain why it would jump into gear.

The truck has no mileage... 49,000 kms or around 30,000 miles. It's been like that since I got it but I wasn't too worried about it because my old car had a bad tranny and I was used to driving like that. Why is it jumping into gears?

 

Sounds like U joints.

 

Huh? A U joint? I don't see how that would affect it at all. But on a side note, the front U joint is new (only a month old).

 

Welcome to the club. But at 30,000 miles? That's weird.

Mine shifts pretty hard (jolts you in your seat pretty good), but mainly at WOT. Other than that, it seems to shift alright. Keep in mind it's pushing 138,000 on the original transmission, so I'm kind of expecting it.

In your case, I'd start with checking the fluid. If the fluid looks good, it sounds like it could be a shift solenoid.