O/D light flashing with rough 2-3 gear shift

where is this solenoid located? inside tranny or outside and is there a picture you can tag to it? Thanks, ready to send this truck off the cliff!

this repair is better done by someone who knows trans. but if you know how to swap trans. that may be an option worth taking. repair to trans done by shop($500or more),vs, swapping trans out yourself($300-$400)