Chrysler Repair: 94 Town & Country shift problem, egr valve, shift problem

Question
My 94 Town and Country minivan with 290K miles had it's 3rd (and final) trany installed at a local shop 3 months ago. It was a 70k mile used OD AT. Van drove fine for about 100 miles. It was parked for 2 months. When I started driving it again I immediately noticed that when driving at a steady speed uphill around 45 mph it would shudder hesitate and "chunk" shifting harshly from 4-3 gear. The "chunk" sounded like a muffled backfire. I added fresh fuel, nothing changed. I checked ATF and it was a little over a pint low so I added Lucas AT fix fluid, no change. I took it back to the shop and they told me the trany gave no codes but that the engine codes indicated a bad EGR valve and bad ground. I replaced the EGR valve and solenoid. The backfire seems to have stopped and it doesn't hesitate/shudder as violently but it still downshifts harshly when going steady uphill.If I push the gas pedal at the bottom of hill it downshifts normally and drives fine uphill in 3rd. Also if I manually put it in 3rd before a hill it drives normally. This makes me doubt that the problem is electrical. Like I said this is the 3rd trany installed and I haven't had this problem before. I have been looking online and now wonder if this could be fluid related. I don't know what fluid the shop used but will ask Monday.
Was it a bad idea to add the Lucas trany fix fluid ?
Have you heard of this uphill downshift problem before ?
Any ideas ?  

Answer
Hi Sean,
Harsh downshifting with that transmission can be caused by:
engine idle speed too high
aerated trans fluid due to too low transfluid level
hydraulic pressure too high internally
valve body malfunction (body can be removed without removing trans, for servicing)
several kinds of internal damage requiring a rebuild

The trans fluid is a sensitive issue with these units. Only use ATF+4 type is the typical recommendation. I don't know whether the Lucas product would be harmful but to get rid of it you would want to flush the entire unit and put in 10 qts of ATF + 4. I don't have a recommendation.
On the fault code question: did they readout from the data link connector that is under the dash? If they used the one in the engine compartment that will only get engine codes. So verify which and be sure to get a readout from the blue plug with 6-pins in a rectangular array that is under the dash on the left side. Let me know any 2-digit codes they get and we'll compare notes.
Roland
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