someotherguy
+1y
Having a custom tune (by people that know what they're doing) is pretty much always going to get you better results than any plug-in programmer.
I haven't had an OBD-II PCM flashed yet but the names I see everybody using are: Wester's Garage, Nelson's Garage, PCM4LESS, Wait4me, may be some others. I'd ask around a bit and see who says what.
You generally have to send off your PCM for them to flash it then send it back. Some of them will offer a service where you pay a deposit and they'll send you the PCM up front, then you get the refund when you send your old one back.
Be sure you talk with them in great detail about what you expect out of the tune. Tell them how you use the truck, whether or not you're open to spending extra for higher grade gasoline (lets them run more spark advance), whether your catalytic converters are still present or if they're removed and the rear O2's aren't hooked up, stuff like that.
You'll probably also want to measure your tire's rolling circumference so you know how big the tire really is, instead of what the manufacturer specs show - not always the same. Mark your tire, and the ground, at exactly 6 o'clock position. Roll the truck so that the mark makes 1 revolution. Mark the ground again at that spot. Measure between, and write that number down. Get your gear ratio number too, which will probably be a 4.10:1 in your case, but check the RPO codes in your glovebox sticker (GT5=4.10). Top gear ratio in your 4L80E is 0.75:1. The reason you want all this crap is so they can be sure your speedometer will be accurate.
Won't change your ability to use a regular scan tool to read codes, sensor data, etc. Whether or not someone's plug-in programmer will still work? I'd guess it should if it just has a scan mode without trying to add its changes to the parameters; I've never used one of those that way so I couldn't tell you for sure.
Richard