I would be leary about any vendor saying they won't hurt the truck. Its not worth the paper its written on. Any modifications can cause a problem if you have parts on the way out already (ie transmission).

I would also suggest the following for your application:

Gauges
3K governor kit
Mild fuel plate.
Intake filter upgrade

Exhaust and the like can come later as you were not after crazy power, stock transmission. The Governor kit and plate will make the truck feel totally different and get rid of the laggy feel. This would be good for around 250RWHP and should be gentle enough to be "safe". Getting the shop in your area to do it is gonna take some research to ensure they know what you are after. The parts are easy to get.

Good luck!