I have a 2000 k2500 (old style) 5.7 208000 mi, that started and ran good for years, sat 3 weeks, cranks but won't start. Fuel pump pressure ( key on) 62# for 1second ,dropping to 58# and holding.Has spark to plugs and the plugs are dry. When cranking 3-4 seconds ,release key to run the engine wil kick back 1 or 2 times ( like chug-chug ). If cranking 8-10 seconds may chug 3-4 times. Once I cranked it about 15+ seconds it started ,went to high idle for 2 seconds and died. Fuel pressure holds at 55-58 over 1/2 hour ( key off ). I need help.