On a new to me '04 Envoy SLT with 101,000 that I bought for my son a month ago I've done the following:
changed oil over to 5W-30 Castrol full synthetic
changed oil filter to K&N
changed transmission fluid
changed front differential fluid using Mobil 1
changed rear differential fluid using Mobil 1
changed transfer case fluid using GM fluid
changed both O2 sensors
changed brake fluid
changed power steering fluid
changed coolant using Prestone Dexcool
changed air filter using Purolator
changed front brakes to ceramic
changed front brake rotors
cleaned throttle body (was bad because PO did it about 10,000 miles ago and wasn't bad)
t-stat was changed by PO 10,000 mile ago (temp goes up and down between 201*-207* at speed using Torque program)
Seafoamed engine twice
ran bottle of Techron through tank of gas
tires are at 36psi and tracks straight as an arrow
First off, thank the Lord for the specials that have been going on at Advance Auto. Between the 40% and 50% off codes I've been doing tons of maintenance to the Voy, '08 Sable with 110,000 miles and '09 Tahoe with 42,000 miles. Secondly, with all that I've done to the Voy the mileage is around 17mpg highway and 14mpg city. I thought it should be higher, especially with the numbers that some people are throwing out here and on the "other" site. Were are into the winter gas here in Iowa so I'm hoping that is what is keeping the mileage down. From what I've read there isn't really anything else I can do maintenance wise to help. If there is, I'm all ears.