55.2-59 59 3100 rear brakes

[2001convertable]

Hi everyone, I did the power brake conversion over the summer. My rear brake have been locking up on a full traffic light or quick stop. I took the truck into a friends shop to have the brakes adjusted which are four wheel drum. After leaving the trouble was still there and the rear brakes are getting hot. The fronts are not getting hot. I was told to install a manual valve on the rear brake line. I bought a wildwood 260-8419 which would cut down to 57% of pressure. Well after the install and a good day I started adjusting. With the valve turned in all the way its still the same. The rear wheels are also still getting hot after a short drive. I checked my e brake cable and they are loose even with no drag. I even shorten the linkage to my new master. I took off my rear drums and used a caliber to get the shoes close.Maybe I need a valve which will give me more than 57%? Im at my Witts end with this. Please if anyone can help.