trans problem 95 Ram 1500

Need help figuring out a problem with the trans in my 95 Dodge Ram, its a 500 or 518 or whatever the overdrive 727 style trans is, problem is it just quit like its in neutral, had to come home on a rollback, unloaded the truck left it sit for a few hours backed down my driveway put it in drive hammered it with the brakes on & it held fine, did this a few times on held it for a long time it would not slip or anything, where do I start looking for the problem, relief valve ? originally I thought that it was low on trans fluid because the dipstick tube oring leaks but I put some in it when it would not drive & it still acted the same.
Any thoughts

Might be the drainback valve in the cooler lines, they have killed more 518s than anything else

Remove the pan and see how much metal is in there plugging up the filter!

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Might be the drainback valve in the cooler lines, they have killed more 518s than anything else

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Quote:

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Remove the pan and see how much metal is in there plugging up the filter!

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Doubt if its junk in the filter, fluid looks fresh & no sparkly stuff
Tell me about the drainback valve, is it part of the cooler lines