Wow, every last one of those things is a "miracle fuel saving device", and pretty much every last one of them does nothing for your fuel economy.
I would spend a little money on an instantaneous mpg computer like the ScanGauge or UltraGauge, then start here:
100+ Hypermiling / ecodriving tips & tactics for better mpg - EcoModder.com
I would put all that crap back on eBay, and save up a few hundred dollars for a set of low rolling resistance tires, some coroplast for the grille, and keep an open mind to upgrading the vehicle to something like a Venture or a Malibu Maxx, as those vehicles can generally do the same job as the Tahoe, but with much higher performance.
And welcome to EcoModder!