What i understand is if i get (4.10)gears for my auto v6. it will need to be tuned again my question is if i get a hand held tuner will i be able to do it myself and where would i plug it in. also how much top speed would i lose

 

It doesn't need to be tuned again but the speedometer will need to be corrected. A flash tuner will do that so you might as well get one, especially since you have an automatic and a tuner is able to change shift points and pressure more to your liking. What year is your vehicle, if it's 99+ the tuner plugs into the OBDII port to the right of your steering column just under the dash. I don't know what you might lose on top speed, but it doesn't matter in my opinion because how often do you drive at top speed?