Transmission troubles

I recently installed a used transmision into a 1995 s-10 blazer 4.3 v6 4x4. I test drove the blazer myself up to 77 miles per hour. Stopped and turned around headed back to my garage and got er up to 80 mph again. No shudders, no slips, no faults. Handed over the keys to the owner that night. he owed me a few more bucks so he drove it up to the local Sunoco store to get change for me. Came back smiling. He drove it the next morning to local walmart store about 10 miles one way fro his place. Then after shopping he drove it down the highway to his home and barely made it to his exit off the highway. The trannsmission just stopped at 65 mph. On the highway. So he coasted it the rest of the way off the highway toward his place. He didn't make it that far. It just stopped when the blazer was done coasting. Stopped dead. So he called me and i drove over to pull it back to my garage to diagnose. Fluid is new and does not smell burnt. Owner claims it never shuddered, never made any loud noises, never clunked. No signs of any trouble other than it just never moved again. No reverse, no forward gears. Could it be that someone else has expirenced this trouble and it results were that the new tranny filter didn't get shoved up in far enough and vibration casused it to fall back out into pan causing trans to suck air in pump instead of solid fluid? I hope? Customer also bought trans from another source.

I recently installed a used transmision into a 1995 s-10 blazer 4.3 v6 4x4. I test drove the blazer myself up to 77 miles per hour. Stopped and turned around headed back to my garage and got er up to 80 mph again. No shudders, no slips, no faults. Handed over the keys to the owner that night. he owed me a few more bucks so he drove it up to the local Sunoco store to get change for me. Came back smiling. He drove it the next morning to local walmart store about 10 miles one way fro his place. Then after shopping he drove it down the highway to his home and barely made it to his exit off the highway. The trannsmission just stopped at 65 mph. On the highway. So he coasted it the rest of the way off the highway toward his place. He didn't make it that far. It just stopped when the blazer was done coasting. Stopped dead. So he called me and i drove over to pull it back to my garage to diagnose. Fluid is new and does not smell burnt. Owner claims it never shuddered, never made any loud noises, never clunked. No signs of any trouble other than it just never moved again. No reverse, no forward gears. Could it be that someone else has expirenced this trouble and it results were that the new tranny filter didn't get shoved up in far enough and vibration casused it to fall back out into pan causing trans to suck air in pump instead of solid fluid? I hope? Customer also bought trans from another source.

Best to start a New thread with you problem.

Yes on the filter.
They make a different filter for deep and shallow pans.
Does it do anything in reverse?

But first make sure fluid level is good when transmission is hot in park engine running.
Make sure engine is still turning converter.
Can you feel anything different when put into reverse or drive?
Is transmission pressure still good or pumping threw cooler line?

Pull pan and check filter and check transmission linkage inside for shifting valve body valve.
And check bottom of pan for any metal.
Let us know what you with these checks.
Does truck hold in park and rool forward in neutral?