tranny problem

2005 silverado 2wh dr 5.3L 1st 2nd work ok. 3rd and D ok up to 18 mph then tranny slipes and whines out.any help

2005 silverado 2wh dr 5.3L 1st 2nd work ok. 3rd and D ok up to 18 mph then tranny slipes and whines out.any help

You need to get it on a transmission/engine capable scanner and read out transmission data and all codes engine/transmission.
Post back code no.

thank you I,ll do that