You can check the transmission fluid for flakes of steel/small steel filings. Other than that, there is no easy (Or cheap) way to check the functionality of your torque converter. Signs of a malfunctioning torque converter can include hesitation or shaking while taking off from a start or difficulty idling while stopped in drive. Although these symptoms can be caused by a malfunctioning torque converter, there are many other things that could make your vehicle act like this so don't immediately rule it out at the torque converter. Only an experienced and honest mechanic can truly tell.
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