Your main problem is likely a wheel that is out of balance. A secondary problem is worn out shocks. Have the front wheels professionally balanced and see if the problem goes away. If not completely gone, replace your front shocks.
I have a 1999 Chevy Suburban LT and if I stay at the recommended hwy speed I easily get 19mpg
Need to know which engine you have.
The oil pressure gauge will fluctuate on a Chevy Tahoe when the vehicle is idling and when the vehicle is driven at highway speed. Idle is usually 30 psi oil pressure or slightly more. At highway speed, the oil pressure should be between 60 psi and 80 psi.
Possibly your speed sensor. My speedometer would bounce around & then soon after it felt like my transmission was slipping. Turns out the speed sensor controls the upshift in your transmission.
Because the vehicle stays at a steady speed and has less starts and stops (at traffic lights).
95.5 mph
i had a ford car that did that and it was the alternater
Here are the actual Specs for a Chevy S-10 17MPG in the city and 24MPG highway if it has an automatic trans with a 2.2L 4 cylinder engine. 20MPG in the city and 26MPG highway if it's a 5 speed manual trans with 2.2L 4 cylinder engine. Now if it has the V6 4.3L engine it gets 15MPG in the city and 20MPG highway with automatic trans. With the manual 5 speed trans it gets 16MPG in the city and 21MPG highway.
I have a 1998 S-10 2.2L 4 cylinder with the standard 5 speed transmission and it gives me 29 mpg highway.
It all depends on the type of highway and the speed limit signs.
A car's engine will turn higher RPM (rotations per minute) on the highway due to the increased speed needed to travel at highway speeds. A car does not need to have it's engine spin at the same RPM level on the city street as it does on the highway.
It is the posted speed.