1996 GMC Sonoma P0300 CYLINDER 6 MISFIRE

This vehicle had the distributor replaced by a G.M. Dealership, due to the cap and rotor melting. Every since then when the vehicle is under load there is a clicking sound from under the hood, { mabey the coil control module/ not sure} the ticking noise corolates with the rpms fluctuating and the check engine light coming on. If I floor the ecelerator it goes away, but if I just hold it steady it keeps on struggling until it is under no load conditions. I have had it to several G.M dealers for repair. They say its fixed, then a couple of days later the problems reaccur. Just about everything I can think of has been replaced in the ignition system. Techs. Keep on telling us they dont know what to do, meanwhile I still have to pay the big bills. Please help. Thanks in advance.