Surprised it didn't come with one in it,but first is it a 4 wheel drive and do you have a long box or short box? If it's a two wheel drive then get a transmission that has a speedo gear so your speedo cable will hook up to it.Have your transmission rebuilt by someone familiar with updates because stock ones had their issues.Make sure you replace the torque converter,and I would also replace the flex plate for good measure.It should bolt right in,however your drive shaft will be the wrong length.If your going to go to all that trouble I would also replace the trans cooler just in case your existing one is contaminated.There is a white plug in just behind the shift lever on the transmission that controls the lock up.Your tranny guy can easily make it so one wire in it can be powered by a switch so you can turn on or of if you like.

Sources: Summit Race Equipment catalogue is a good guide.