No more "same shop"... Not for that tranny anyway, they don't know what they're doing with the Dodge Diesel OD at least. My opinion of course.
It could be as simple as a dirty ground. Could be the TPS, it is not supposed to be servicable but many people have taken them apart, cleaned them up and adjusted more voltage and been back in business. I would search the Diesel Truck Resource and the Turbo Diesel Register and do a potentiometer modification rather then fool with the TPS ever again. A new TPS is over $200 and less than $300, I forget the actual amount, Sorry. A potentiometer modification is under $5 bucks, read that five bucks.
There are upgrade parts available to allow more fluid to get to the OD section of the trans. which has been a problem, I would talk to someone about that. And you can have that OD section rebuilt seperate if necessary. Dave Goerand is good people, he specializes in Dodge diesel transmissions and converters. They are very busy I have found, and do not always return calls or email quickly. But they are very knowledgeable.