If he is ordering a thottle cable, that means that yours somehow has phyical damage. Maybe it is crimped and now sticking? That would be odd. Usually, when the tranny starts that upshift/downshift crap it can be a couple of things:
1. Govenor Pressure Solenoid is getting crap stuck to it - means that the front clutch pack is going away and debris is getting circulated throughout the tranny and eventually finding its way to the solenoid.
2. Govenor Pressure Transducer has crap going through it for the same reason as above, and now it is giving intermittent false reading causing the ECU to vary the pressure back and forth making it do the crazy shifting.
3. You have a fairly massive internal valvebody or clutch pack piston seal leak causing the pressure to vary inside of the tranny and it is simply reacting to the pressure changes.
4. Shift cable could, I suppose, be kinked and responding slowly to the action of the throttle body. But as long as the cable is not broken in two, and it is adjusted right, it would not downshift, then upshift, and then downshift again all at wide open throttle due to a cable issue.
My guess is it is a combination of 1 and 2 and can be resolved by replacing the Govenor Solenoid and Transducer. Now, as far as the cause of the drebris, you will soon need a tranny rebuild and some mods to make it last longer.