Transmision not working properly. on 2006 Dodge Ram 1500

Sometimes it will work fine and others it will not shift to 1st. Also at times it will not shift into overdrive. I think the code said it was the shift sensor, if so where is it lcated and how hard is it to change?

Asked by for the 2006 Dodge Ram 1500
seek a free diag and est from aamco. DO NOT TRY TO REPAIR YOURSELF
1 more answer , 1 more comment
bring to tranny shop for diagnostic. more thorough.
check fluid level. may be low. if dark in color, may be due for change. if milky or muddied, then fluid is contaminated. tranny tech. will advise.
Thanks For Your Help.