Here goes... We have a 1998 durango, 5.2, 4wd, 44re transmission. The original transmission went out at about 150,000 miles. Went to advanced and ordered a new reman transmission. $1600 later we got the transmission and hooked back up to the engine. Filled it up partway and started it up and put into neutral, found out the case was cracked so we took it out and sent it back. New transmission showed up (january) and now I believe this one is starting to go.

When shifted into reverse or manual low, the durango will shudder, drop to about 300 rpm then it'll die, about 75% of the time. If you shift into drive or 2, everything operates like normal. At one point in time the o2 sensor failed throwing a code and got that fixed but the problem still exists.

The transmission fluid level is fine, not burnt smelling or discolored (still cherry red). From what I've been told, the problem is within the reverse/low clutch pack. Could that be the cause of this? The transmission is still under warranty but I doubt I will send it back in for a new one seeing as this is the second one I've received.

If its still under warranty, I'd send it back and get another. No reason not to that I know of.

sorry but the units that Advance and the other chain parts stores sell are not very good units.
You would be better off finding a good local repair facility to handle the job.

Was the cooler flow tested???

Yeah, did that between the swap from the 1st to 2nd transmission

First, if you shift into low or reverse, and the car is not moving, does the problem occur then? If so, it is a torque converter issue, probably in the lockup area. At idle, in any gear, and the car not moving, the input shaft should not be turning, and torque converter slippage should let the engine idle with minimal drag. Having the trans scanned may show up that the computer is trying to lock the converter up for some reason. Second, if the problem occurs as you are moving in manual low or reverse, then it probably is either the low/reverse BAND (there is no low/reverse CLUTCH) and/or the over running clutch (rear sprag) is failing. Both would have to occur for the problem to happen in both rev and man low. Even if the low/rev band was slipping the rear sprag should hold for a clean first gear. A better description of what is happening is needed.

I have not had good luck with advance auto trans, and they try to skate the warranty due to instalation error

I agree it sounds like a convertor issue.

In first or reverse it will shift slowly in gear and will kill the engine before you can get moving. If you give it some gas while it's shifting you can get it to move with some ferocious jerking internally.

what went bad on the original trans, just burnt out, did you do fluid changes?

The original one had originally started slipping around 140,000 and made it to 150,000 slipping on a 1-2 shift. Then it received some abuse in winter time getting stuck on the road. When it finally gave out it was all burnt up. Last fluid change on the original was around 100,000.

Also: Today put it on ramps and unplugged the transmission electrical connectors that run up to the computer. While it was in limp-in mode, it experienced the same problems as before. That should eliminate the computer as being the problem, leading it back to some sort of engine/transmission type of deal.

Plugged cooler,loop the cooler lines together and see if it helps.Big problem with transmission coolers in the factory radiators.I never use a old cooler with a rebuilt transmission,bypass original radiator and run an stand alone cooler.