Two 80E Questions
Second, with a good fresh 80E (either stock low miles or good fresh OE rebuild), what kind of power capacity can I expect?
Yes it will work with a relay. Contact slow67 for details, he has a nice write-up and instructions.
Fresh or good condition stock 4L80E is good for about 450-500 HP/TQ. Some hydraulic mods will make it good for 700-800ish depending on combo.

