HOW TO FIX A 2003 JEEP GRAND CHEROKEE?

HAVE A 2003 JEEP GRAND CHEROKEE WITH 4.0 LITRE 6 IN IT. ENGINE IS TRYING TO SHUT DOWN. WILL BE RUNNING FINE, THEN ENGINE WILL BEGIN TO MISS, GAS GAUGE WILL DROP TO ZERO, CAN ADD RPMS TO ENGINE, ENGINE WILL SMOOTH OUT, DOES NOT DO ALL THE TIME, RUNS FINE IN THE EARLY MORNING HOURS, GIVE TROUBLE IN LATER HOURS OF DAYWHEN OUTSIDE TEMP HEATS UP, LIVE IN MOBILE , ALABAMA, THE MORE GAS IN TANK RUNS BETTER, LESS THAN 1/4 TANK RUNS BAD,HAVE CHANGE FUEL FILTER, CHECK ENGINE LIGHT DOES NOT COME ON, NO ENGINE CODES FOUND, WHATS WRONG?

E KING
October 2008