You also have to change the pcv valve, it makes a huge difference when you're getting up in miles.
Change the fuel filter
My guess would be wheel balance.
check your oil lol
Could be a faulty spark plug or spark plug wire.
try checking your mass air flow sensor or just change it.
your heater core is going out, you need to replace it before it ruptures.
The Trailblazer has more expensive trim and options. It's designed to appeal to a slightly more affluent market segment than the Blazer.
i accidentally hit the button sometimes and dont know it til i am going. a few times i have gotten into 4low because i hit the button and as i was switching to drive, i passed neutral and it jumped. my 95 you had to hesitate on neutral.
pOSSSIBLE RELAY PROBLEM
The voltage gauge on the Blazer is not the most accurate (cheap) When using the signals the voltage draw on the system is enough to make the gauge move slightly.
Your description indicates a problem with the fuel delivery system, first check the fuel filter it may be clogging, also the fuel pump may be getting weak and not able to deliver adequite fuel pressure during high demand.
Worn right front wheel bearing.