Re your cranking problems when hot. On a fully charged battery check the voltage drop and current draw. It should not go below 9.6 volt while cranking. A fully charged battery that reads 13v or better doesn't mean it can deliver the amps. Charge it and do a load test @ 3 times the amp rating for 15 seconds. ( 80 amp x 3 = 240 amp ), Voltage should not drop below 9.6 volts. If it passes check all starter cables and grounds. If that's good buy a good quality brand name starter.