Alright every time i start cruising the RPM's are around 900. Once i put the brake on the RPM's instatnly drop to 550. i let go of the brake it goes back up to 900. Happens everytime I dont know if this is normal since i havent got my truck back for about 4 months. Just wondering what it can be

That's normal. When coasting, the engine sort of freewheels, when you press the brakes, it loads the power steering pump (feeding the hydroboost), and since the injection pump is only supplying idle fuel quantity, the engine returns to idle speed.

Mine does the same thing, although once I release the brake it stays at 550-600 until I hit the accelerator pedal.