Transmission problem

[cux]

Hi have a 1986 K5: 350/700R4/33"
I pay a guy to rebuild my transmission and I have the problem that when I start using the truck every thing’s fine but after 10 minutes the transmission STOP working, I don’t know why, I wait 30 minutes and the transmission works again for another 10 minutes.
Any Idea
PLEASE HELP!!!

 

[hidesertwheelin]

What do you mean it stops working? It won't shift or it wont go at all?

 

[cux]

it wont go at all not even revese

 

[GMC1977]

fluid level? filter may have fallen off in the pan? bad modulator? take it back and have the guy fix it

 

[cux]

fluid level? filter may have fallen off in the pan? bad modulator? take it back and have the guy fix it

fluid is ok the first thing he chack yas the fileter and it's ok
I'm gonna check the modulator.

thanks