ok, 2001 hyundai elantra,
Having trouble shifting, (automatic) Im having "shift flares" like car
doesnt know what speed im going, ill be doing 60 in like third gear and
the rpm are at 4000!

So the dealer recomend I change the speed sensors, I did, somewhere
else and te problem came back weeks later, so now they say its the
transmission control module. Which is more rare and way more expensive,
Would it be a good idea to put in a used TCM or should I get a brand
new one?

This car is a pain but I dont have enough money to get a new one!

The guys who repaced my speed sensors said it was a daunting task, Now
I want to know if the TCM is as well, because I want to just buy an old
one and put it in myself and save myself money and time.