Chevrolet Repair: 1999 Chevrolet 3500, spark plug wire, compression tester

Question
I have a 1999 Chevrolet 3500 with the 5.7 in it, i was pulling my boat from the lake one day and it all the sudden had a loss of power, going up any incline the passing gear would kick in and it would start back firing and popping and there was no power.  I recently changed the plugs and plug wires to try to fix it but its still got a miss and backfires under a load and at an ideal it is running real rich.  Without the boat behind it it runs better but you still can hear a miss.  Any advice would be greatly appreciated,  thanks again

Answer
HI MARSHALL, WELL YOU SAY THAT THE ENG IS MISFIRING... THE REASON YOU FEEL IT MORE WITH YOUR BOAT IS BECAUSE IT IS JUST LOADING THE ENG DOWN THAT MUCH MORE... WHAT YOU NEED TO DO IS START THE ENG AND HAVE SOMEONE PUT THE TRANSMISSISON IN GEAR AND RAISE THE IDLE JUST ENOUGH TILL IT STARTS TO MISFIRE OR [SKIP]. NOW YOU REMOVE 1 SPARK PLUG WIRE AT A TIME WITH A RUBBER PAIR OF PLIERS OR INSULATED PLIERS WHAT EVER AND WHEN YOU REMOVE EACH WIRE PAY CLOSE ATTENTION TO THE ONE THAT HAS NO EFFECT ON THE ENG IDLE. THIS IS WHERE THE PROBLEM IS. THIS CYLINDER IS NOT DOING ANYTHING AT ALL. [DEAD CYLINDER] WHEN YOU REMOVE A SPARK PLUG WIRE THAT HAS A GOOD CYLINDER YOU WILL FEEL THE ENG START TO SKIP WORSE THEN IT IS,SO YOU KNOW THAT CYLINDER IS FIRING OK..PUT THE WIRE BACK ON AFTER CHECKING OF COURSE. SO LETS SAY YOU FIND THE CYLINDER THAT IS NOT FIRING,NOW YOU WILL NEED TO FIND OUT IF IT IS FUEL,IGNITION,DIST-CAP CRACKED OR INTERNAL PROBLEM. SUCH AS BAD VALVE...BEST THING TO DO IS TO GET BACK TO ME WHEN YOU HAVE FOUND THE BAD CYLINDER AND THEN I WILL GO ON FROM THERE...WILL NEED TO KNOW IF YOU HAVE ANY TOOLS SUCH AS COMPRESSION TESTER,LEAK DOWN GAUGE..LET ME KNOW.