E-Brake engaging

[GreaseTrain]

I have a 98 5.7 Silverado with the Z71 package. The E-Brake will engage while I'm in reverse. Seems to do it mostly if I'm on uneven ground, backing up quicker than an idle, or if I'm turning. I'm pretty sure it's the E-Brake because when it'll engage and the truck will come to a stop, if I push the E-Brake in it'll slam on more, then when I pull the release I'll be able to continue backing up... until it does it again, pretty soon if i'm turning, on uneven ground or going faster than idle.

 

Has anyone come across this???