why is truck hard to crank on 1997 Chevrolet 1500 Pickup

truck hass 300,000 miles on it and when it sits for a few day and you try to crank it it turns over fine for 10 seconds but doesnt crank. and then it starts jumping as if it isnt realsing the compression or something what could this be from?

Asked by for the 1997 Chevrolet 1500 Pickup
explain turns over for 10 sec but doesn't crank? do you mean turns over but doesn't start.if so ck fuel pressure.waht motor do you have?