transmission trouble

three months ago i went in for an oil change at a lube shop. they accidently pulled my transmission plug and refilled it. the problem started recently with my transmission slipping and a mechanic looked at the fluid and could tell by the color that the transmission fluid was dark and a new one was needed. i tallked to the lube place but they claim they did nothing wrong since the car just went over 100k miles. is there anything they could have done to cause the transmission to go out or was it coincidental. also my idle has recently been really low and there is a winding sound in 1st and 2nd gear. alot of info i know just wanted some expert advice thanks. jon

I dont see why flushing the tranny fluid would casue the problem because i went to i lube place and they told i should have it done.I'd take it to a shop that speacilizes in transmissions to get it checked out.Regular mechanics might just wanna rip you off.

There is a possibility that the lube shop mechanics accidentally or intentionally placed something inappropriate to your transmission. You have mentioned that they accidentally pulled out your transmission plug and they refilled it, when they refilled the transmission oil did you see what type of oil they used?