02 brake question

I have an 02 Tacoma 4x4 4cyl, 5 speed all stock. disc on front , drum on rear. no abs. I have had the truck for 4 months. twice now i have come up to a stop and the brake pedal feels like it wont even depress, very high and hard and there are almost no brakes. After coming to a (very slow) stop, they go back to normal and dont do it again? any thoughts? I talked to the orig owner and he said it did it with him a few times too.

 

Vacuum lines going into the booster maybe? check the caliper pins as well. Meaning the pins the brake pads ride on. Sometimes those rust and stick the pads in place.