Allison troubles

[DVT873]

You didn't say but I'm guessing this is a 3000 series? TCM's are a problem but since you swapped and it is still acting up that is probably not it. Had one this spring. Started shifting oddly/badly. Customer thought they could "drive the problem away" No. Trans was trashed internally. Do you have a computer and a connection device like an Insite Inline 6 or a Nexiq? Codes can also be accessed in the shift selector. Post a picture of the shifter. You should be a Gen4/5 shifter. Could still be Gen 3. Code access is a little different. Should be able to find something on you tube or google about that.

These are pretty well protected but they do have internal solenoid and wiring issues. Did the Allison dealer find any codes? What were they if they did? I would try and check codes. are you getting a trans warning light? Solenoid and wiring usually provide some helpful codes.

Another thing that may be happening is the TCM may be getting bad information. Like there is an ABS or traction control event when there isn't. This usually just affects torque converter lockup. To see all that would require Allison DOC or an equivalent scan tool that can see live data.

But. The surest bet is to drop the pan and look inside. There are two filters in the bottom of the pan. Odd thing is these don't always show a lot of trash in the fluid or in the filters. This is because there is a third filter on top of the valve body. It hides under a cap. It does a GREAT job of holding trash back. To see it you have to drop the valve body. Not too bad a job, make sure you unplug the harness. Careful it is heavy. Once it is down there will be three bolts and the cover will come off. If I had better pics I can't find them.
You can't really see it but there was a 2 inch mound of metal and powdered metal inside.

If you are in NE Ohio there is a very good Allison shop in Youngstown. Some good long term guys including a father and son team. Other than them I don't know. Like everything else ability to figure out what is wrong then fix it correctly is lost. Most don't give a shi#t.