abs lock up?

 1996 jimmy 4x4 when stopping on wet or slippery roads the brakes lock up and stay that way, till i put it in reverse and then they let go,no lights on dash or codes set,i pulled the abs fuses and it does not happen,not shure if its a sensor or mabey the controller,any ideas what could cause this?

You're going to have to get the ABS codes read, sounds like a problem in the control module.

When was the last time you did a brake service?
You could be having a caliper that is hanging up.

brakes where serviced few mounths ago,there not the problem,work fine when the abs is unplugged,found out its the left front wheel that locks up and wount relese,not the calaper or any thing there,the abs moter runs and the truck stops fine,but the left wheel wount un lock,fooled arond with the dump valves by pushing them in and out and it let go,run fine stoped fine,seems when it locks up  and i push pull the dump valve stems it releases, is this something that can be changed?or rebuilt,could it be the way the brakes where bled when  the master was replaced?or do i have to change the whole unit out?

Yeah, sounds like your ABS valve assembly has messed up...  Its not going to be a cheap repair, but you can find rebuilt units on the internet.