So I have a question that I'm probably going to be hung out to dry for.

Not only is it NOT about a third gen vehicle, it's about a TRUCK (perish the thought!)

However, this board is filled with extremely knowledgeable folks, and I was hoping one of you fine gents might be able to shed some light on the topic.

I've done a lot of reading in the DIY PROM and this board about ECM tuning, enough to know most "performance chips" are infact pretty useless, and just advance your engine's timing and up the fuel ratios a bit. However, I have a friend who is looking to get one of these chips, primarily to recalibrate his speedo post-lift and whatnot and perhaps to get a little added performance out of his '08 GMC with a 5.3 motor in it.

Do any of you know what brands are reputable, and whether or not one of these chips will even affect his speedometer? New cars are strange, terrible voodoo to me, but I'd like to be able to impart to him some useful advice, as I myself have been burned numerous times by shoddy deals due to ignorance.

 

An 08 is OBDII which requires the pcm to be sent to a tuner (Blackbear is highly regarded) or a programmer such as the diablo or sct. Most (if not all) programmers allow you to change the speedo calibration though.