[John Poling]

Eljaro,

No experience here with the Flywheel/Starter interference when hot, but I would doubt that is your problem.
What gauge cable are you using from you battery to your solenoid and from you solenoid to your starter? What gauge of cable are you using from the frame to your battery? Do you have a heavy ground strap running from you engine block to your frame? Are all of your connections clean? I would suggest removing all of your connections and cleaning them to bare metal and then applying a dielectric sealing grease on all cable connections except on your battery, this should be available at NAPA. Also, why do you think your solenoid is good? The magnetic part may be working fine but you may have burned/corroded contacts inside that may not allow enough current flow when it gets hot.

John