buick regal 3.8 knocking/pinging

I have a 93 Buick Regal GS w/ a 3.8 & 4t60e tranny. I have had a problem for a while with the car pinging/ knocking when the car is going up hills(not very steep ones at that). I believe the tranny is locked up at the time. Usually going around 40-45 mph. I have replaced the EGR thinking that could be the cause, but no change. Tried higher octane gas which didn't help either. I tried one of those cheap code readers from a local auto parts place and it flashes a code 39. According to the book, that is a knock sensor problem or tcc clutch problem. I am not sure where the knock sensor is located on this engine or I would just replace it since it isn't that expensive. I didn't think it is common for those to fail. Should I just replace the sensor or maybe the TCC solenoid? Is it a major ordeal to replace the solenoid? Or maybe someone has another idea. Thanks for your help.