[RahX]

The torque converter's job is to provide a fluid couple from the engine to the internals of the transmission. If something is wrong with the converter it will make noise/vibrate, the torque converter clutch will not lock in or pop in and out (500rpm difference max if it has one), have lack of power/no power, or leak. I'm not sure about your trans as far as how/what operates it as far as the electronics or lack thereof but it sounds like it is defaulting to 2nd/3rd due to heat or slippage.