Ok, so I reverse into the driveway, shut off the motor, and put the tranny in 1st to keep the truck ON the driveway. But, it can rock forward and if pushed you can get it to roll down the driveway. With the tranny in 1st. And I hear/feel the pistons moving in the motor.

Does this sound like bad compression to you (a.k.a. bad headgasket)? I would imagine that good compression means no rolling in first gear. Also, the e-brake is misadjusted and doesn't hold for squat.

 

My truck does the same thing if the parking brake is not on. I have never checked the compression, but it has done that for at least 9 or 10 years.

Your rear brakes probably need an adjustment for the parking brake to work, and the automatic adjuster might not be working. Checking the rear brake shoes and wheel cylinders would also be a good idea.

 

Mine will slowly roll forward as well. We just need a parking brake.

 

not to answer your actual question, maybe parking with transmission in reverse gear will solve the symptoms.

 

im no experts but the valves would open and close while you pushed it so wouldnt that be why you can hear the pistons moving

 

Nothing wrong with your truck, this is a normal event. If there is enough slope and no parking brake, the weight of the truck will cause the vehicle to slowly roll down the slope. Fix your parking brake, or put the truck in reverse if you usually back in.