Finally... after two rebuilds, I had enough and tore into it myself. Ever since my original rebuild in June 2017, my truck shuttled between 1-2 at 10mph under light throttle. Parking lot, traffic, etc... resting foot on pedal, reach 10mph, 2-1-2-1-2, if I pressed the pedal hard enough to shift at say 1800RPMs, it would shift fine.

Fast forward to August 2018, reverse went out... just under 2 months past warranty on my transmission, another rebuild since it broke the rear band, still shuttling. I read up on the issue awhile back, finally decided to dig into myself. The problem mostly seems to manifest in the 48RE behind diesels, but I can attest it happens in the whole range of RE!

The magic fix was a Borg Warner Heavy Duty governor pressure solenoid, part number 50185, found one on Ebay for $35, totes worth it.

FRJRTmk.jpg

This is the part, the OEM Mopar one is on the right with the blue o-rings, the Borg Warner unit is on the left with black o-rings. There's only two "gotcha" points on installing. You have to make sure it snaps in and the retainer goes in the groove against the cylinder, NOT the 2nd groove (there's a youtube video by cascade explaining this is a common user error on install). The other one is the plug is actually inverted, when you install it, you have to flip the wiring harness over. Please make sure the retainer clip is on the same side as the tab. I also changed out the 3-4 accumulator spring while I was in there, the one installed looked almost the same, but I put the Sonnax .126" HD in anyway. I bought it, Imma use it!

Now at light throttle, it waits until about 13mph and drops into 2nd without a second thought. I also thought that it would only affect 1-2 shifts, but now my entire range shifts like cold butter, firm but smooth. At lighter throttle it's not mushy or lazy, just quick and done. Under heavy throttle, you get a solid fast upshift, no clunking. Noted transmission response is better as well, it doesn't hesitate to downshift when I jab the gas and does it faster. Used to be when I'd go WOT, it'd take a second before semi-lazy downshifting, now it just snaps down a gear before the pedal reaches the floor.

Will my results be the same for everyone? Likely not. Is this the definite fix for 1-2 shuttle? Nah, could be a front band adjustment for you. If you have the transmission pan off already should you get one? Yes. It's cheaper than a Mopar one, and much better, very easy to change as well. My truck is a 1998 Dakota with a 3.9L V6 and 42RE auto transmission. All of this info should be the same for the entire line of Magnum engines and matching auto trans. (3.9: 42RE, 5.2: 44RE, and 5.9: 46RE)

Quick how-to on changing:

1: Suggest putting truck in the air, via jack stands or (as I did) ramps.
2: Engage parking brake, chocks in the back, standard safety.
3: Begin slowly removing the transmission pan bolts, 13MM, along one side with catch-pan underneath try not to let the full weight hold along one side to bend the pan.
4: With a hand under the pan, remove the rest of the bolts, tilt pan to dump remaining fluid into catch pan, leave catch pan under to catch drippage from transmission.
5: Clean up yourself a bit, this is a messy job. Also clean the pan and magnet.
6: The solenoid block is on the passenger side, to remove there's four 7/16" bolts, and two T25 Torx screws. (In my 98, there was no retainer section for the transducer, I only had to remove three of the 7/16" bolts and the two Torx ones).
7: Very gently pull down on the retainer, or remove the retainer and pull on the solenoid to pop it out. Be VERY gentle, it shouldn't be hard, you don't want to damage the wiring harness.
8: The harness catch, you gently lift the middle tab over the retainer catch and pull the harness out.
9: Reverse the process with the Borg Warner solenoid, I flipped the wiring harness and attached it, then snapped the solenoid in before sliding the retainer back around to ensure it was fully seated.
10: Pan bolts in a cross pattern torque 6 ftlb, 9 ftlb, then 12 ftlb. (The people who rebuilt my trans stripped two of my bolt holes :/ I had to just draw them up, doesn't seem to leak at least, next time the pan comes off, helicoil job.)
11: Refill trans. (I reused my fluid since it was only a week old, ran it through a coffee filter for any particles.)

Bonus: 3-4 Accumulator spring
1: Follow above to 5.
2: Remove filter, it's held on by two T25 Torx, keep catch pan under it.
3: There's a plate with five T25 torx bolts and a hook, the wiring is held by this hook. Remove the bolts slowly.
4: Keep your hand on the plate when you remove the last screw, the plate, spring, and piston will fall out.
5: Reverse for install.

Hopefully this helps someone if they drift by via Google, or actual users of this forum. I'm just disappointed that the old motto fell into place... "If you want something done right, you have to do it yourself." Two rebuilds and I still had to do this to make it shift right.