if you check out their website you can see more specific details but to answer your questions -
- diffefence between powerpup and GT - GT has a display to monitor ecu parameters, power pup does not
- triple dog is the GT, no difference
- there is a separate unit called the WATCHDOG which is just the display with monitoring features, no tuning capabilities.
- the powerpup and GT only work with 05+ models
- they are both very simple to use, no tuning knowledge required. get the GT though it will be useful having the display and a better resale value. you'll be able to sell it for what you paid for if you buy it used. they generally go for $275-$300 (average) on here, or you can buy new from one of the supporting vendors on here.
good luck, don't be intimidated its an easy process and it will really wake your truck up.