I have the SuperChips programmer for my 97, and I'm very happy with it. Nothing to install. Easy to use. Easy to re-program to stock if need be, and comes with I believe less than 6 setting, but it has 'extreme' which I use, as well as a 'tow-safe' and 'economy' setting.
Since I have it together with propane - I also installed a very simple shift-kit, to reduce slipping. I'm not sure if anyone can answer how many HP you can safely run through your tranny. Lots of torque is even worse, but the transmissions are strong. Obviously you will wear it out if you keep pulling through the gears under full load - all day every day.
As you get used to your truck, you also learn when it shifts, so you let up for a millisecond, to help it. (As long as you have a shift-kit - so you can feel it. Stock is just too sloppy)
Fuel economy. My SuperChips programmer helped a little, so did better intake and exhaust. I'll get 19 mpg at around 75 - and it'll drop to 17 if I'm at 85-90 - which I believe to be well over 1 mph/gallon better than stock (but not 4-5 mpg like I get the feeling that some people like to claim/believe)
For years I measured every time I filled - and since I did mods not all at once, I just kept seeing slightly better and better figures - while the engine becoming more perky with each mod - also, so the total is worth the effort.
My best readings are over 20, and one just over 21 mpg, but that's on slow windy roads, but hilly, and all the way up to 9,800 feet, so I was impressed.
As soon as you start making mods, you'll see what works - and what you like.