If I turn on either right or left turn signal,the fronts work fine but both rear signals blink together.I checked the bulbs,replaced flashers and replaced turn signal switch,nothing works.Hazards work fine.Also if the signal is turned on and the brakes applied all the signals stay on until brake released.Any ideas .Thanks...

Welcome to AF!
Sounds to me like you might have troubles with trailer wiring. Check to see if your truck has been wired with a trailer plug. You could find one or more wires shorted together.

Thanks for the idea.I did put in a trailer light wiring kit 4 years ago.Someone else mentioned this also so I disconnected the harness but did not help.I will have to look more closely at it.Thanks...