Delayed transmission engagemnet after parked for extended time on Dodge Ram Van B250

Problem Description and Possible Solution
Delayed transmission engagement of 2 to 8 seconds may be noted after  the vehicle has been parked for an extended period. Our technicians tell the repair involves installing a drainback relief valve in the transmission oil cooler pressure line.
Problem Data
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Average mileage: 159,000 (158,000–160,000)
Drive Train affected: Automatic Transmission
2 model years affected: 1991, 1994
3 people reported this problem
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Viewing 1 - 2 of 2 comments
I just experienced this problem last week for the first time.
What happens is after I place my shifter into park, the van rolls forward or backward depending on the slope. There is a loud thumping sound till I step on the brake and try to get the shifter into a locking position.
This never happened before in the 17 years I had this van.
My engine is running in good order and the transmission runs very well.
I hate the idea of keeping 2 bricks in the van to block off the wheels when I park.
If there is a solution or a source for repair please touch base A.S.A.P.
I have this problem presently. After sitting over night the van is subject to an 8 to 10 second delay in transmission engagment. The delay is longer, when it is colder