aamco transmission sold a transmission without a proper inspection, transmission is now slipping after 5,000 km edmonton, Alberta

BUYER BEWARE. I bought a used transmission from AAMCO in Edmonton Alberta and had it installed in my 98 dodge ram for just over $1,700.00 6 months, 5,000 km later the tranny is slipping and will not shift into OD until it has warmed up. At the point of purchase I was assured they inspect the tranny. silly me assumes this means they inspect it like they inspected my old transmission to diagnose it and ensure the internals are good. nope! they just take off the pan and look at the fluid. now I am out $1,700.00 and only got 5000 km out of the tranny. they offered to look at it for free, but I will then need to purchase another transmission or rebuild the one I bought 5000 km ago.He had said it could be a sensor, but it is doing the exact same thing the previous trannydid before I lost all my gears. thanks aamco.