ICM, coil dis,? Back Firing issues

[ROBSHAFER]

Hello all hope someone can help because this is weird and I've been chasing this issue for over a year.. I have a 1996 maxum with a 5.7 merc. The engine is new, (issues started after swap)the fuel pump, coil,  distributor and all the wiring is original. trying to fix this issue. new wires, plugs, cap,rotor, choke, alternator, battery . Cleaned tank pickup in line filters, checked anti siphon . What I have finally discovered. After running hard for half and hour or more, Something (electrical I think) gets hot and i get a back fire through carb. pop pop. Once it starts it gets worse and worse at any speed, until I'm force to run at idle speed with no issues. If i run at idle speed for an hour or so or sit with engine off for a good amount of time over half an hour. it runs better pops are less frequent. So heres where its weird. the last time this happened I was trying different ranges of speed to see if i could get it to run smooth faster then an idle. What I discovered is the second  I hit the tilt button it would back fire. So it appears something gets hot and a drop in voltage causes it to malfunction on demand instead of occasionally when its having trouble. IDEAS ??? I haven't checked loose connections, plugs, grounds, as electrical didn't dawn on me until the tilt thing. Thanks for the help<br><br>